config: replace deprecated use of AC_OUTPUT with AC_CONFIG_FILES

Signed-off-by: Gaetan Nadon <memsize@videotron.ca>

configure.ac

@@ -86,8 +86,9 @@ AC_SUBST([moduledir])
 DRIVER_NAME=fbdev
 AC_SUBST([DRIVER_NAME])
 
-AC_OUTPUT([
+AC_CONFIG_FILES([
                 Makefile
                 src/Makefile
                 man/Makefile
 ])
+AC_OUTPUT