[SCSI] mvumi: Use PCI_VENDOR_ID_MARVELL_EXT for 0x1b4b

With the 0x1b4b vendor ID #define in place, convert hard-coded ID
values.

Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: James Bottomley <James.Bottomley@hansenpartnership.com>