mpt3sas: Eliminate dead sleep_flag code

With the exception of a single call to wait_for_doorbell_int(), all this
conditional sleeping code is dead. So delete it.

Signed-off-by: Calvin Owens <calvinowens@fb.com>
Acked-by: Chaitra P B <chaitra.basappa@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>