scsi: mpt3sas: fix possible memory leak.

In ioctl exit path driver refers ioc_list to free memory associated with
diag buffers and event_log pointer used to save events by driver.
If ctl_exit() func is called after unregistering driver, then ioc_list will
be empty and hence driver will not be able to free the allocated memory
which in turn causes memory leak.
So call ctl_exit() function before unregistering mpt3sas driver.

Signed-off-by: Chaitra P B <chaitra.basappa@broadcom.com>
Signed-off-by: Suganath Prabu S <suganath-prabu.subramani@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>