mpt3sas: Never block the Enclosure device

Never block the SEP device (i.e. Never invoke the
scsi_internal_device_block() API for SEP device) even for the delay not
responding events. Blocking the SEP device will create a deadlock while
adding any device to the OS.

Signed-off-by: Suganath prabu Subramani <suganath-prabu.subramani@avagotech.com>
Signed-off-by: Chaitra P B <chaitra.basappa@avagotech.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>