ipr: set scsi_level correctly for disk arrays

Set the scsi_level correctly for disk arrays such
that things like the rotational field get set
properly by sd.c.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Reviewed-by: Wen <Xiong&lt;wenxiong@linux.vnet.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>