test/cmd-discard: use correct skip exit value

It's T_EXIT_SKIP, not T_SETUP_SKIP.

Fixes: 244be25 ("test: add discard cmd tests")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

test/cmd-discard.c

@@ -347,7 +347,7 @@ int main(int argc, char *argv[])
 	int cmd_op;
 
 	if (argc != 2)
-		return T_SETUP_SKIP;
+		return T_EXIT_SKIP;
 	filename = argv[1];
 
 	fd = open(filename, O_DIRECT | O_RDONLY | O_EXCL);