tty: ipwireless: Fix potential NULL pointer dereference

tty: ipwireless: Fix potential NULL pointer dereference

BugLink: https://bugs.launchpad.net/bugs/1863019
[ Upstream commit 7dd50e205b3348dc7784efbdf85723551de64a25 ]

There is a potential NULL pointer dereference in case
alloc_ctrl_packet() fails and returns NULL.

Fixes: 099dc4fb6265 ("ipwireless: driver for PC Card 3G/UMTS modem")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>