vrend: Use regular blit if both buffers are sRGB

We don't need to use gl blend if both source and target buffers are in sRGB
and colorspace transformation isn't requiqred. Fixes this test:
dEQP-GLES3.functional.fbo.blit.conversion.srgb8_alpha8_to_srgb8_alpha8

Tested-by: Jakob Bornecrantz <jakob@collabora.com>
Reviewed-by: Jakob Bornecrantz <jakob@collabora.com>
Signed-off-by: Jakob Bornecrantz <jakob@collabora.com>

src/vrend_renderer.c

@@ -5906,7 +5906,8 @@ static void vrend_renderer_blit_int(struct vrend_context *ctx,
        !vrend_format_is_ds(dst_res->base.format))
       use_gl = true;
 
-   if (util_format_is_srgb(src_res->base.format))
+   if (util_format_is_srgb(src_res->base.format) &&
+       !util_format_is_srgb(dst_res->base.format))
       use_gl = true;
 
    /* different depth formats */