[SCSI] eata_pio: off by one in eata_pio_detect()

Smatch complains that the reg_IRQ[] array only has MAXIRQ (16) elements
so we are one space beyond the end of the array here.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>