mesa-dri-glsl-native: Avoid error when running configure a second time

This avoids the error:

ln: creating symbolic link `/media/data1/build1/poky/build/tmp/work/x86_64-linux/mesa-dri-glsl-native-7.11-r0/Mesa-7.11/src/glsl//../../configs/current': File exists

---
 .../mesa/mesa-dri-glsl-native_7.11.bb              |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

index 07b0761..9194595 100644
@@ -17,7 +17,7 @@ inherit native
 
 # use default config for native build
 do_configure_prepend() {
-	ln -s ${S}/../../configs/default ${S}/../../configs/current
+	ln -sf ${S}/../../configs/default ${S}/../../configs/current
 }
 
 do_install() {