vrend: Correctly set pack alignment for three component textures

For rgb8 and rgb16 textures the element size is 3 and 6 respectively,
and the packing must correspond to the component size (1 and 2).

Fixes:
  dEQP-GLES3.functional.texture.specification.basic_teximage3d.rgb16i_3d
  dEQP-GLES3.functional.texture.specification.basic_teximage3d.rgb16ui_3d
  dEQP-GLES3.functional.texture.specification.basic_teximage3d.rgb8i_3d
  dEQP-GLES3.functional.texture.specification.basic_teximage3d.rgb8ui_3d

Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Signed-off-by: Jakob Bornecrantz <jakob@collabora.com>

src/vrend_renderer.c

@@ -6156,9 +6156,11 @@ static void vrend_resource_copy_fallback(struct vrend_resource *src_res,
    } else {
       switch (elsize) {
       case 1:
+      case 3:
          glPixelStorei(GL_PACK_ALIGNMENT, 1);
          break;
       case 2:
+      case 6:
          glPixelStorei(GL_PACK_ALIGNMENT, 2);
          break;
       case 4:
@@ -6192,9 +6194,11 @@ static void vrend_resource_copy_fallback(struct vrend_resource *src_res,
    glPixelStorei(GL_PACK_ALIGNMENT, 4);
    switch (elsize) {
    case 1:
+   case 3:
       glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
       break;
    case 2:
+   case 6:
       glPixelStorei(GL_UNPACK_ALIGNMENT, 2);
       break;
    case 4: