V4L/DVB (6391): bttv: SPICT ioctl doesn't work with vlc

The bttv driver instists that the depth specified in the call to VIDIOCSPICT
match the pixel format specified in the same call.

vlc doesn't set the depth field, which makes the SPICT ioctl always fail.

The V4L1 standard is not clear on how most operation are supposed to work, and
this is no exception.  The depth field would appear to be entirely redundant,
as the pixel format specifies a specific depth.  It could be that this field
was only meant for output from the *G*PICT ioctl and should be ignored in
*S*PICT.  This is in fact what the v4l1-compat wrapper does.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>