media: cx231xx: Fix recursive dependency

0day build bot reported an unnoticed recursive dependency, fix it
by removing the select statement.

fixes: c66d4d99a8fb ("cx231xx: Add I2C_MUX dependency")

Signed-off-by: Brad Love <brad@nextdimension.cc>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>