mesa: remove duplicate assignments in bind_xfb_buffers()

Useless to do that before checking errors. It's now similar to
the other bind_XXX_buffers() helpers.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/mesa/main/bufferobj.c

@@ -4055,9 +4055,6 @@ bind_xfb_buffers(struct gl_context *ctx,
       GLsizeiptr size = 0;
 
       if (range) {
-         offset = offsets[i];
-         size = sizes[i];
-
          if (!bind_buffers_check_offset_and_size(ctx, i, offsets, sizes))
             continue;