skeleton: fix VCS folders not being excluded from rootfs

There is a typo in skeleton.mk preventing rsync from excluding VCS
folders such as .svn.

Signed-off-by: Nathan Ford <nford@westpond.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/skeleton/skeleton.mk

@@ -78,7 +78,7 @@ endef
 endif
 
 define SKELETON_INSTALL_TARGET_CMDS
-	rsync -a --ignore-times $(SYNC_VCS_EXCLUSIONS) \
+	rsync -a --ignore-times $(RSYNC_VCS_EXCLUSIONS) \
 		--chmod=u=rwX,go=rX --exclude .empty --exclude '*~' \
 		$(SKELETON_PATH)/ $(TARGET_DIR)/
 	$(call SKELETON_USR_SYMLINKS_OR_DIRS,$(TARGET_DIR))