sgiioc4: fix error cleanup path (take 2)

The driver "forgot" to call iounmap() iff request_mem_region() call failed in
sgiioc4_ide_setup_pci_device()...

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Cc: jeremy@sgi.com
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>