scsi: qla2xxx: Fix for double free of SRB structure

commit bcc71cc3cde1468958a3ea859276d8d1a1a68265 upstream.

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: 726b8548 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>