fs: descend into sub directories when it is necessary

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/fs/cramfs/Makefile b/fs/cramfs/Makefile
index e2b2c73..12d73a3 100644
--- a/fs/cramfs/Makefile
+++ b/fs/cramfs/Makefile
@@ -5,5 +5,5 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-$(CONFIG_CMD_CRAMFS) := cramfs.o
-obj-$(CONFIG_CMD_CRAMFS) += uncompress.o
+obj-y := cramfs.o
+obj-y += uncompress.o