vmwgfx: fix missing array notation

Fixes error identified by gcc-12.1.0 compiler

make
  CC       libvmwgfx_la-vmwgfx_tex_video.lo
vmwgfx_tex_video.c: In function 'stop_video':
vmwgfx_tex_video.c:240:20: error: the comparison will always evaluate as 'true' for the address of 'yuv' will never be NULL [-Werror=address]
  240 |                if (priv->yuv[i]) {
      |                    ^~~~

vmwgfx/vmwgfx_tex_video.c

@@ -237,7 +237,7 @@ stop_video(ScrnInfoPtr pScrn, pointer data, Bool shutdown)
 
        for (i=0; i<3; ++i) {
 	   for (j=0; j<2; ++j) {
-	       if (priv->yuv[i]) {
+	       if (priv->yuv[j][i]) {
 		   xa_surface_destroy(priv->yuv[j][i]);
 		   priv->yuv[j][i] = NULL;
 	       }