scsi: qla2xxx: Fix duplicate switch database entries

The response data buffer used in switch scan is reused 4 times.  (For example,
for commands GPN_FT, GNN_FT for FCP and FC-NVME) Before driver reuses this
buffer, clear it to prevent duplicate entries in our database.

Fixes: a4239945 ("scsi: qla2xxx: Add switch command to simplify fabric discovery"
Cc: <stable@vger.kernel.org>
Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Reviewed-by: Ewan D. Milne <emilne@redhat.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>