[media] v4l: tvp5150: Fix comment regarding output pin muxing

The FID/GLCO/VLK/HVLK and INTREQ/GPCL/VBLK pins are muxed differently
depending on whether the input is an S-Video or composite signal. The
comment that explains the logic doesn't reflect the code. It appears
that the comment is incorrect, as disabling the output data bus in
composite mode makes no sense. Update the comment to match the code.

While at it define macros for the MISC_CTL register bits, the code is
too confusing with numerical values.

Cc: stable@vger.kernel.org # For Kernel	4.5 and	upper
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>