V4L/DVB (4712): Fix warning when compiling on x86_i64

drivers/media/dvb/dvb-usb/usb-urb.c: In function 'usb_allocate_stream_buffers':
drivers/media/dvb/dvb-usb/usb-urb.c:125: warning: format '%u' expects type 'unsigned int', but argument 4 has type 'long long unsigned int'

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>