mwifiex: check wait_event_interruptible return value

wait_event_interruptible function returns -ERESTARTSYS if it's
interrupted by a signal. Driver should check the return value
and handle this case properly.

In mwifiex_wait_queue_complete() routine, as we are now checking
wait_event_interruptible return value, the condition check is not
required. Also, we have removed mwifiex_cancel_pending_ioctl()
call to avoid a chance of sending second command to FW by other path
as soon as we clear current command node. FW can not handle two
commands simultaneously.

Cc: "3.6+" <stable@vger.kernel.org>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>