media: usbtv: Enforce standard for color decoding

Depending on the chosen standard, configure the decoder to use the
appropriate color encoding standard (PAL-like, NTSC-like or SECAM).

Until now, the decoder was not configured for a specific color standard,
making it autodetect the color encoding.

While this may sound fine, it potentially causes the wrong image tuning
parameters to be applied (e.g. tuning parameters for NTSC are applied to
a PAL source), and may confuse users about what the actual standard is
in use.

This commit explicitly configures the color standard the decoder will
use, making it visually obvious if a wrong standard was chosen.

Signed-off-by: Hugo Grostabussiat <bonstra@bonstra.fr.eu.org>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>