usb: f_gsi: Fix BUG_ON for calling sleeping function in invalid context

In Current code driver calling spin_lock_irqsave two time with
different lock. This will lead an issue where irqs remains disabled
on processor. After that calling queu_work function reporting bug with
sleeping function called from invalid context.

Fix this by using spin_lcck instead of spin_lock_irq_save.

Change-Id: I68f05283fe541eb5af123a4ce836ee0fc1dd7e48
Signed-off-by: Chandana Kishori Chiluveru <cchiluve@codeaurora.org>