mtd: tmio_nand.c: use dev_get_platdata() and resource_size()

Remove unnecessary casts and use dev_get_platdata() to retrieve the
struct mfd_cell data from the platform.

Use resource_size() for the ioremap()'s.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>