submodule--helper: don't use bitfield indirection for parse_options()

submodule--helper: don't use bitfield indirection for parse_options()

Do away with the indirection of local variables added in
c51f8f94e5b (submodule--helper: run update procedures from C,
2021-08-24).

These were only needed because in C you can't get a pointer to a
single bit, so we were using intermediate variables instead.

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
Signed-off-by: Junio C Hamano <redacted>
Signed-off-by: Glen Choo <redacted>
Signed-off-by: Junio C Hamano <redacted>