media: tc358743: Return an appropriate colorspace from tc358743_set_fmt

media: tc358743: Return an appropriate colorspace from tc358743_set_fmt

When calling tc358743_set_fmt, the code was calling tc358743_get_fmt
to choose a valid format. However that sets the colorspace
based on information read back from the chip, not the colour
format requested.

The result was that if you called try or set format for UYVY
when the current format was RGB3 then you would get told SRGB,
and try RGB3 when current was UYVY and you would get told
SMPTE170M.

The value programmed in the VI_REP register for the colorspace
is always set by this driver, therefore there is no need to read
back the value, and never set to REC709.
Return the colorspace based on the format set/tried instead.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>