mfd: Use resource_size() in sm501

The requested memory region is smaller than the actual ioremap().
Use resource_size() to get the correct size.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>