Fix: Don't build the whole helper/ when only the helper protocol libr…

…ary is needed

Without this patch the helper binary is built even when
`BUILTIN_HELPER` is set to false (i. e. when an external helper is
selected with configure).

Signed-off-by: Paul Wolneykien <manowar@altlinux.org>

src/Makefile.am

@@ -172,7 +172,7 @@ if HAVE_PASSWD_HELPER
 mate_screensaver_dialog_LDADD +=	\
 	../helper/libhelper-proto.a
 ../helper/libhelper-proto.a:
-	$(MAKE) -C ../helper
+	$(MAKE) -C ../helper libhelper-proto.a
 endif
 
 BUILT_SOURCES = 		\