locks: fix generic_delete_lease tracepoint to use victim pointer

It's possible that "fl" won't point at a valid lock at this point, so
use "victim" instead which is either a valid lock or NULL.
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>

fs/locks.c

@@ -1728,7 +1728,7 @@ static int generic_delete_lease(struct file *filp, void *owner)
 			break;
 		}
 	}
-	trace_generic_delete_lease(inode, fl);
+	trace_generic_delete_lease(inode, victim);
 	if (victim)
 		error = fl->fl_lmops->lm_change(victim, F_UNLCK, &dispose);
 	spin_unlock(&ctx->flc_lock);