st/mesa: fix texture buffer objects

Broken by 624528834f.

Reviewed-by: Brian Paul <brianp@vmware.com>

src/mesa/state_tracker/st_atom_texture.c

@@ -234,12 +234,18 @@ update_single_texture(struct st_context *st,
    }
 
    /* Determine the format of the texture sampler view */
+   if (texObj->Target == GL_TEXTURE_BUFFER) {
+      view_format =
+         st_mesa_format_to_pipe_format(stObj->base._BufferObjectFormat);
+   }
+   else {
       view_format = stObj->pt->format;
 
       /* If sRGB decoding is off, use the linear format */
       if (samp->sRGBDecode == GL_SKIP_DECODE_EXT) {
          view_format = util_format_linear(view_format);
       }
+   }
 
    /* if sampler view has changed dereference it */
    if (stObj->sampler_view) {