fs: descend into sub directories when it is necessary

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/fs/reiserfs/Makefile b/fs/reiserfs/Makefile
index 55f70b1..5a692f0 100644
--- a/fs/reiserfs/Makefile
+++ b/fs/reiserfs/Makefile
@@ -9,4 +9,4 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-$(CONFIG_CMD_REISER) := reiserfs.o dev.o mode_string.o
+obj-y := reiserfs.o dev.o mode_string.o