pong-clock: Fix LICENSE field

Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

meta/recipes-graphics/pong-clock/pong-clock_1.0.bb

@@ -1,5 +1,5 @@
 DESCRIPTION = "A clock combined with a game of pong"
-LICENCE = "GPLv2"
+LICENSE = "GPLv2+"
 DEPENDS = "virtual/libx11 xdmcp xau"
 
 SRC_URI = "file://pong-clock-no-flicker.c"
@@ -13,4 +13,4 @@ do_compile () {
 do_install () {
 	install -d ${D}${bindir}
 	install -m 0755 pong-clock ${D}${bindir}
-}
+}