mpt3sas: Eliminate conditional locking in mpt3sas_scsih_issue_tm()

This flag that conditionally acquires the mutex is confusing and prone
to bugginess: refactor it into two separate function calls, and make the
unlocked one complain if it's called outside the mutex.

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>