scsi: qla2xxx: Avoid that issuing a LIP triggers a kernel crash

Avoid that issuing a LIP as follows:

  find /sys -name 'issue_lip'|while read f; do echo 1 > $f; done

triggers the following:

BUG: unable to handle kernel NULL pointer dereference at (null)
Call Trace:
 qla2x00_abort_all_cmds+0xed/0x140 [qla2xxx]
 qla2x00_abort_isp_cleanup+0x1e3/0x280 [qla2xxx]
 qla2x00_abort_isp+0xef/0x690 [qla2xxx]
 qla2x00_do_dpc+0x36c/0x880 [qla2xxx]
 kthread+0x10c/0x140

[mkp: consolidated Mauricio's and Bart's fixes]

Signed-off-by: Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>
Reported-by: Bart Van Assche <bart.vanassche@sandisk.com>
Fixes: 1535aa75 ("qla2xxx: fix invalid DMA access after command aborts in PCI device remove")
Cc: Himanshu Madhani <himanshu.madhani@cavium.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>