mfd: use pci_ioremap_bar() in sm501

Use the newly introduced pci_ioremap_bar() function in drivers/mfd.
pci_ioremap_bar() just takes a pci device and a bar number, with the goal
of making it really hard to get wrong, while also having a central place
to stick sanity checks.

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Samuel Ortiz <sameo@openedhand.com>