st/mesa: don't do srgb->linear conversion in decompress_with_blit

This fixes piglit/getteximage-formats on r600g.

NOTE: This is a candidate for stable branches.

Reviewed-by: Brian Paul <brianp@vmware.com>
(cherry picked from commit 5e7e7d96b3)

src/mesa/state_tracker/st_cb_texture.c

@@ -639,6 +639,7 @@ decompress_with_blit(struct gl_context * ctx,
 
       u_sampler_view_default_template(&sv_temp, stObj->pt, stObj->pt->format);
 
+      sv_temp.format = util_format_linear(sv_temp.format);
       sv_temp.u.tex.first_level =
       sv_temp.u.tex.last_level = texImage->Level;