V4L/DVB (5591): Saa7146: proper prototype for saa7146_video_do_ioctl()

This patch adds a proper prototype for saa7146_video_do_ioctl() in
include/media/saa7146_vv.h.

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>