qla2xxx: Fix stale pointer access.

qla2xxx: Fix stale pointer access.

[ Upstream Commit 84e32a06f4f8756ce9ec3c8dc7e97896575f0771 ]

Commit 84e32a0 ("qla2xxx: Use pci_enable_msix_range() instead of
pci_enable_msix()") introduced a regression when target mode is enabled.
In qla24xx_enable_msix(), ha->max_rsp_queues was incorrectly set
to a value higher than the number of response queues allocated causing
an invalid dereference. Specifically here in qla2x00_init_rings():
    *rsp->in_ptr = 0;

Add additional check to make sure the pointer is valid. following
call stack will be seen

---- 8< ----
RIP: 0010:[<ffffffffa02ccadc>]  [<ffffffffa02ccadc>] qla2x00_init_rings+0xdc/0x320 [qla2xxx]
RSP: 0018:ffff880429447dd8  EFLAGS: 00010082
....
Call Trace:
[<ffffffffa02ceb40>] qla2x00_abort_isp+0x170/0x6b0 [qla2xxx]
[<ffffffffa02c6f77>] qla2x00_do_dpc+0x357/0x7f0 [qla2xxx]
[<ffffffffa02c6c20>] ? qla2x00_relogin+0x260/0x260 [qla2xxx]
[<ffffffff8107d2c9>] kthread+0xc9/0xe0
[<ffffffff8107d200>] ? flush_kthread_worker+0x90/0x90
[<ffffffff8172cc6f>] ret_from_fork+0x3f/0x70
[<ffffffff8107d200>] ? flush_kthread_worker+0x90/0x90
---- 8< ----

Cc: <stable@vger.kernel.org>
Signed-off-by: Quinn Tran <quinn.tran@qlogic.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@qlogic.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>