KVM: Fix spinlock taken warning during host resume

KVM: Fix spinlock taken warning during host resume

 WARNING: CPU: 0 PID: 13554 at kvm/arch/x86/kvm//../../../virt/kvm/kvm_main.c:4183 kvm_resume+0x3c/0x40 [kvm]
  CPU: 0 PID: 13554 Comm: step_after_susp Tainted: G           OE     5.1.0-rc4+ #1
  RIP: 0010:kvm_resume+0x3c/0x40 [kvm]
  Call Trace:
   syscore_resume+0x63/0x2d0
   suspend_devices_and_enter+0x9d1/0xa40
   pm_suspend+0x33a/0x3b0
   state_store+0x82/0xf0
   kobj_attr_store+0x12/0x20
   sysfs_kf_write+0x4b/0x60
   kernfs_fop_write+0x120/0x1a0
   __vfs_write+0x1b/0x40
   vfs_write+0xcd/0x1d0
   ksys_write+0x5f/0xe0
   __x64_sys_write+0x1a/0x20
   do_syscall_64+0x6f/0x6c0
   entry_SYSCALL_64_after_hwframe+0x49/0xbe

Commit ca84d1a24 (KVM: x86: Add clock sync request to hardware enable) mentioned
that "we always hold kvm_lock when hardware_enable is called.  The one place that
doesn't need to worry about it is resume, as resuming a frozen CPU, the spinlock
won't be taken." However, commit 6706dae9 (virt/kvm: Replace spin_is_locked() with
lockdep) introduces a bug, it asserts when the lock is not held which is contrary
to the original goal.

This patch fixes it by WARN_ON when the lock is held.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Fixes: 6706dae9 ("virt/kvm: Replace spin_is_locked() with lockdep")
[Wrap with #ifdef CONFIG_LOCKDEP - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>