The check for the mux_signal callback was wrong which prevents us to
configure the 6pin port's FSR/CLKR signal mux.
Reported-by: CF Adad <cfadad@rocketmail.com> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com> Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com> Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com> Cc: stable@vger.kernel.org (3.4+)