platform/chrome: cros_ec_typec: Tolerate unrecognized mux flags

On occasion, the Chrome Embedded Controller (EC) can send a mux
configuration which doesn't map to a particular data mode. For instance,
dedicated Type C chargers, when connected, may cause only
USB_PD_MUX_POLARITY_INVERTED to be set. This is a valid flag combination
and should not lead to a driver abort.

Modify the mux configuration handling to not return an error when an
unrecognized mux flag combination is encountered. Concordantly, make the
ensuing print a debug level print so as to not pollute the kernel logs.

Cc: Keith Short <keithshort@chromium.org>
Signed-off-by: Prashant Malani <pmalani@chromium.org>
Acked-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Benson Leung <bleung@chromium.org>
Link: https://lore.kernel.org/r/20201106020305.767202-1-pmalani@chromium.org