usb: dwc3: gadget: add missing spin_lock()

usb: dwc3: gadget: add missing spin_lock()

commit 5c7b3b02de766a8634708953e805399e3544a290 upstream.

commit 8e74475b0e0a (usb: dwc3: gadget: use udc-core's
reset notifier) added support for the new UDC core's
reset notifier to dwc3 but while at it, it removed
a spin_lock() from dwc3_reset_gadget() which might
cause an unbalanced spin_unlock() further down the line

Fixes: 8e74475b0e0a (usb: dwc3: gadget: use udc-core's reset notifier)
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>