bnxt_en: Fix a possible NULL pointer dereference in unload path

bnxt_en: Fix a possible NULL pointer dereference in unload path

In the driver unload path, the driver currently checks the valid
BNXT_FLAG_ROCE_CAP flag in bnxt_rdma_aux_device_uninit() before
proceeding.  This is flawed because the flag may not be set initially
during driver load.  It may be set later after the NVRAM setting is
changed followed by a firmware reset.  Relying on the
BNXT_FLAG_ROCE_CAP flag may crash in bnxt_rdma_aux_device_uninit() if
the aux device was never initialized:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
PGD 8ae6aa067 P4D 0
Oops: 0000 [#1] SMP NOPTI
CPU: 39 PID: 42558 Comm: rmmod Kdump: loaded Tainted: G           OE    --------- -  - 4.18.0-348.el8.x86_64 #1
Hardware name: Dell Inc. PowerEdge R750/0WT8Y6, BIOS 1.5.4 12/17/2021
RIP: 0010:device_del+0x1b/0x410
Code: 89 a5 50 03 00 00 4c 89 a5 58 03 00 00 eb 89 0f 1f 44 00 00 41 56 41 55 41 54 4c 8d a7 80 00 00 00 55 53 48 89 fb 48 83 ec 18 <48> 8b 2f 4c 89 e7 65 48 8b 04 25 28 00 00 00 48 89 44 24 10 31 c0
RSP: 0018:ff7f82bf469a7dc8 EFLAGS: 00010292
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000206 RDI: 0000000000000000
RBP: ff31b7cd114b0ac0 R08: 0000000000000000 R09: ffffffff935c3400
R10: ff31b7cd45bc3440 R11: 0000000000000001 R12: 0000000000000080
R13: ffffffffc1069f40 R14: 0000000000000000 R15: 0000000000000000
FS:  00007fc9903ce740(0000) GS:ff31b7d4ffac0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000992fee004 CR4: 0000000000773ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
 bnxt_rdma_aux_device_uninit+0x1f/0x30 [bnxt_en]
 bnxt_remove_one+0x2f/0x1f0 [bnxt_en]
 pci_device_remove+0x3b/0xc0
 device_release_driver_internal+0x103/0x1f0
 driver_detach+0x54/0x88
 bus_remove_driver+0x77/0xc9
 pci_unregister_driver+0x2d/0xb0
 bnxt_exit+0x16/0x2c [bnxt_en]
 __x64_sys_delete_module+0x139/0x280
 do_syscall_64+0x5b/0x1a0
 entry_SYSCALL_64_after_hwframe+0x65/0xca
RIP: 0033:0x7fc98f3af71b

Fix this by modifying the check inside bnxt_rdma_aux_device_uninit()
to check for bp->aux_priv instead.  We also need to make some changes
in bnxt_rdma_aux_device_init() to make sure that bp->aux_priv is set
only when the aux device is fully initialized.

Fixes: d80d88b0dfff ("bnxt_en: Add auxiliary driver support")
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>