reset.c: move update_index_refresh() call out of read_from_tree()

reset.c: move update_index_refresh() call out of read_from_tree()

The final part of cmd_reset() essentially looks like:

  if (pathspec) {
    ...
    read_from_tree(...);
  } else {
    ...
    reset_index(...);
    update_index_refresh(...);
    ...
  }

where read_from_tree() internally also calls
update_index_refresh(). Move the call to update_index_refresh() out of
read_from_tree for symmetry with the 'else' block, making
read_from_tree() and reset_index() closer in functionality.

Signed-off-by: Martin von Zweigbergk <martinvonz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>