[media] cx231xx: stop double error reporting

i2c_mux_add_adapter already logs a message on failure.

Reviewed-by: Wolfram Sang <wsa@the-dreams.de>
Reviewed-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Peter Rosin <peda@axentia.se>