usb: udc: core: add device_del() call to error pathway

commit c93e64e91248becd0edb8f01723dff9da890e2ab upstream.

This patch fixes a bug in the error pathway of
usb_add_gadget_udc_release() in udc-core.c.  If the udc registration
fails, the gadget registration is not fully undone; there's a
put_device(&gadget->dev) call but no device_del().

Acked-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Felipe Balbi <balbi@ti.com>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>