[media] tc358743: Setup default mbus_fmt before registering

Previously the mbus_fmt_code was set after the device was
registered. If a connected sub-device called tc358743_get_fmt
prior to that point it would get an invalid code back.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>