[SCSI] ipr: Fixup device type check

Fixup a check used by the ipr driver to determine if a given
device is a SCSI disk. Due to the addition of support for
attaching SATA devices, this check needs to be more robust.

Signed-off-by: Brian King <brking@us.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>