fs_mgr: turn on -Werror

- deal with some -Wunused-variable issues

Change-Id: Ie0140d4777ddf862e4bbed76142a1dbb8320c1b0
diff --git a/fs_mgr/Android.mk b/fs_mgr/Android.mk
index 165ebd4..7cffc37 100644
--- a/fs_mgr/Android.mk
+++ b/fs_mgr/Android.mk
@@ -11,6 +11,7 @@
 LOCAL_STATIC_LIBRARIES := liblogwrap libmincrypt libext4_utils_static
 LOCAL_C_INCLUDES += system/extras/ext4_utils
 LOCAL_EXPORT_C_INCLUDE_DIRS := $(LOCAL_PATH)/include
+LOCAL_CFLAGS := -Werror
 
 include $(BUILD_STATIC_LIBRARY)
 
@@ -31,5 +32,7 @@
 
 LOCAL_STATIC_LIBRARIES := libfs_mgr liblogwrap libcutils liblog libc libmincrypt libext4_utils_static
 
+LOCAL_CFLAGS := -Werror
+
 include $(BUILD_EXECUTABLE)