scsi: mpt3sas: memset request frame before reusing

Driver gets a request frame from the free pool of DMA-able request frames
and fill in the required information and pass the address of the frame to
IOC/FW to pull the complete request frame. In certain places the driver
used the request frame allocated from the free pool without completely
clearing the previous data stored in it. The request contents were cleared
only for the size of the new request to be issued and that left out some
stale data in the unused part of the request. Though the IOC/FW is not
expected to access the request beyond the specified size, it is good
practice to clear complete request message frame.

So reinitialize the complete request message frame with 0s before using
it.

Signed-off-by: Suganath Prabu <suganath-prabu.subramani@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>