fbset-modes: fix a warning about not existant S

Set the S variable to $WORKDIR to remove the warning about S being not
existant

Signed-off-by: Chunrong Guo <B40290@freescale.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>

meta-oe/recipes-support/fbset/fbset-modes.bb

@@ -6,6 +6,7 @@ PV = "0.1.0"
 PR = "r6"
 
 SRC_URI = "file://fb.modes"
+S = "${WORKDIR}"
 
 do_install() {
     install -d ${D}${sysconfdir}