[SCSI] mpt2sas: Do not call sas_is_tlr_enabled for RAID volumes.

For RAID volume sas_is_tlr_enabled call will hit BUG at
scsi_transport_sas.c:163, since raid volume
is not visible to sas transport layer.
Now Added check to make sure arg pass in sas_is_tlr_enabled() is not a volume.

Signed-off-by: Kashyap Desai <kashyap.desai@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>