mfd: sta2x11-mfd: Do not mind about gpio platform data

The gpio platform driver will take care of its platform data,
let's not do any checks here.

Signed-off-by: Davide Ciminaghi <ciminaghi@gnudd.com>
Acked-by: Alessandro Rubini <rubini@gnudd.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>