[SCSI] hpsa: use check_signature

Use check_signature to find a signature in the mmio address.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Mike Miller <mike.miller@hp.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>