usb: dwc3: gadget: Release spinlock to allow timeout

Since spinlock is locked, jiffies does not update
during the loop iterations. If the break condition
is never met, we get stuck in an infinite loop.
Releasing the spinlock solves this issue.

Change-Id: I420c825ce006d976e819793eb569013de87cfc40
Signed-off-by: Bar Weiner <bweiner@codeaurora.org>