Fixed order of usb_alloc_urb pointer validation.

Cc: Luca Risolia <luca.risolia@studio.unibo.it>
Signed-off-by: NDouglas Schilling Landgraf <dougsland@linuxtv.org>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>