intel: silence a compiler warning

Silence

  warning: ‘buf_format’ may be used uninitialized in this function
diff --git a/icd/intel/cmd_meta.c b/icd/intel/cmd_meta.c
index 12081b4..fdf5289 100644
--- a/icd/intel/cmd_meta.c
+++ b/icd/intel/cmd_meta.c
@@ -636,6 +636,8 @@
         buf_format = XGL_FMT_R32G32B32A32_UINT;
         break;
     default:
+        img_format = XGL_FMT_UNDEFINED;
+        buf_format = XGL_FMT_UNDEFINED;
         break;
     }