[SCSI] libsas: Warn if ATA device detected but CONFIG_SCSI_SAS_ATA not set

We give a very cryptic error if an ATA device is seen on a SAS port
but libsas isn't compiled to include libata to handle them.  Add an
extra warning to explain specifically what the problem is.

Acked-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>