[SCSI] Use pcibios_resource_to_bus()

We had our own code (pci_get_base_address()) to get the bus address of
a BAR.  We can get this using pcibios_resource_to_bus() instead.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>