usb: u_bam: Fix spinlock leak followed by lockup from workqueue

Driver has missing code to release spinlock while returning from
workqueue in case of memory allocation failures.
Returning from workqueue without releasing spinlock messes up
with worker thread and kernel keeps throwing up warnings like:
"BUG: workqueue leaked lock or atomic: kworker/u" for any
sleeping function called from worker thread afterwards. Later
when driver again tries to acquire same (unreleased) spinlock
it results in spinlock lockup.

CRs-Fixed: 497158
Change-Id: I4eaa7aaa42ed95a9b78a8939e80f4c0694e574b2
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>