qed: Fix missing error code in qed_slowpath_start()

The error code is missing in this code scenario, add the error code
'-EINVAL' to the return value 'rc'.

Eliminate the follow smatch warning:

drivers/net/ethernet/qlogic/qed/qed_main.c:1298 qed_slowpath_start()
warn: missing error code 'rc'.
Reported-by: NAbaci Robot <abaci@linux.alibaba.com>
Fixes: d51e4af5 ("qed: aRFS infrastructure support")
Signed-off-by: Nchongjiapeng <jiapeng.chong@linux.alibaba.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/qlogic/qed/qed_main.c

@@ -1299,6 +1299,7 @@ static int qed_slowpath_start(struct qed_dev *cdev,
 			} else {
 				DP_NOTICE(cdev,
 					  "Failed to acquire PTT for aRFS\n");
+				rc = -EINVAL;
 				goto err;
 			}
 		}