[SCSI] mpt2sas: Removed redundant global mutex for IOCTLs

When the lock_kernel and unlock_kernel routines were removed in the
2.6.39 kernel, a global mutex was added on top of the existing mutex
which already existed. With this implementation, only one IOCTL
will be active at any time no matter how many ever controllers
are present. This causes poor performance.

Removed the global mutex so that the driver can work with the existing
semaphore that was already part of the existing code.
Signed-off-by: Nagalakshmi Nandigama <nagalakshmi.nandigama@lsi.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>