scsi: qla2xxx: Fix panic in qla_dfs_tgt_counters_show

When trying to display tgt_counters in the debugfs, a panic can result.

There is no null check for qpair after it is assigned in the for-loop.
Unless vha->hw->queue_pair_map array is completely filled with entries, the
system will panic dereferencing a null pointer.
Signed-off-by: Bill Kuzeja <william.kuzeja@stratus.com>
Acked-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/qla2xxx/qla_dfs.c

@@ -193,6 +193,8 @@ qla_dfs_tgt_counters_show(struct seq_file *s, void *unused)
 
 	for (i = 0; i < vha->hw->max_qpairs; i++) {
 		qpair = vha->hw->queue_pair_map[i];
+		if (!qpair)
+			continue;
 		qla_core_sbt_cmd += qpair->tgt_counters.qla_core_sbt_cmd;
 		core_qla_que_buf += qpair->tgt_counters.core_qla_que_buf;
 		qla_core_ret_ctio += qpair->tgt_counters.qla_core_ret_ctio;