submodule: don't use submodule_from_name

The function 'submodule_from_name()' is being used incorrectly here as a submodule path is being used instead of a submodule name. Since the correct function to use with a path to a submodule is already being used ('submodule_from_path()') let's remove the call to 'submodule_from_name()'. Signed-off-by: Brandon Williams <bmwill@google.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>