wlcore: unlock on error in wl1271_op_suspend()

We recently introduced a new error path which needs an unlock.

Fixes: 6d5a748d ('wlcore: add ability to reduce FW interrupts during suspend')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>