scsi: qla2xxx: Fix for double free of SRB structure

scsi: qla2xxx: Fix for double free of SRB structure

This patch fixes issue during switch command query where driver was freeing
SRB resources multiple times

Following stack trace will be seen
[  853.436234] BUG: unable to handle kernel NULL pointer dereference at
0000000000000001
[  853.436348] IP: [<ffffffff811df514>] kmem_cache_alloc+0x74/0x1e0
[  853.436476] PGD 0
[  853.436601] Oops: 0000 [#1] SMP

[  853.454700]  [<ffffffff81099f6a>] ? mod_timer+0x14a/0x220
[  853.455543]  [<ffffffff81185465>] mempool_alloc_slab+0x15/0x20
[  853.456395]  [<ffffffff811855a9>] mempool_alloc+0x69/0x170
[  853.457257]  [<ffffffff81098af2>] ? internal_add_timer+0x32/0x70
[  853.458136]  [<ffffffffc0092d2b>] qla2xxx_queuecommand+0x29b/0x3f0 [qla2xxx]
[  853.459024]  [<ffffffff8146535a>] scsi_dispatch_cmd+0xaa/0x230
[  853.459923]  [<ffffffff8146e11f>] scsi_request_fn+0x4df/0x680
[  853.460829]  [<ffffffff81029557>] ? __switch_to+0xd7/0x510
[  853.461747]  [<ffffffff812f7113>] __blk_run_queue+0x33/0x40
[  853.462670]  [<ffffffff812f7735>] blk_delay_work+0x25/0x40
[  853.463603]  [<ffffffff810a882a>] process_one_work+0x17a/0x440
[  853.464546]  [<ffffffff810a94f6>] worker_thread+0x126/0x3c0
[  853.465501]  [<ffffffff810a93d0>] ? manage_workers.isra.24+0x2a0/0x2a0
[  853.466447]  [<ffffffff810b099f>] kthread+0xcf/0xe0
[  853.467379]  [<ffffffff810b08d0>] ? insert_kthread_work+0x40/0x40
[  853.470172] Code: db e2 7e 49 8b 50 08 4d 8b 20 49 8b 40 10 4d 85 e4 0f 84 20
01 00 00 48 85 c0 0f 84 17 01 00 00 49 63 46 20 48 8d 4a 01 4d 8b 06 <49> 8b 1c
04 4c 89 e0 65 49 0f c7 08 0f 94 c0 84 c0 74 ba 49 63
[  853.472072] RIP  [<ffffffff811df514>] kmem_cache_alloc+0x74/0x1e0
[  853.472971]  RSP <ffff88103726fc50>

Fixes: 726b85487067 ("qla2xxx: Add framework for async fabric discovery")
Cc: <stable@vger.kernel.org>
Signed-off-by: Giridhar Malavali <giridhar.malavali@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>