[SCSI] mpt fusion: convert inactive_list_mutex to a mutex

the semaphore inactive_list_mutex is used as a mutex, convert it to
the mutex API

Signed-off-by: Matthias Kaehlcke <matthias@kaehlcke.net>
Acked-by: "Moore, Eric" <Eric.Moore@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>