usb: dwc3: ep0: fix compile warning

commit 34c60a7 (usb: dwc3: ep0: tidy up Pending
Request handling) introduced a compile warning
by leaving an unused variable.

This patch fixes that warning:

drivers/usb/dwc3/ep0.c: In function ‘__dwc3_gadget_ep0_queue’:
drivers/usb/dwc3/ep0.c:129:8: warning: unused variable ‘type’
[-Wunused-variable]

Signed-off-by: Felipe Balbi <balbi@ti.com>