st/vega: Silence uninitialized variable warning.

Fixes this GCC warning.
api_filters.c: In function 'execute_filter':
api_filters.c:184: warning: 'tex_wrap' may be used uninitialized in this function

src/gallium/state_trackers/vega/api_filters.c

@@ -207,6 +207,7 @@ static void execute_filter(struct vg_context *ctx,
       break;
    default:
       debug_assert(!"Unknown tiling mode");
+      tex_wrap = 0;
       break;
    }