log_ref_setup: don't return stack-allocated array

log_ref_setup: don't return stack-allocated array

859c301 (refs: split log_ref_write logic into log_ref_setup,
2010-05-21) refactors the stack allocation of the log_file array into
the new log_ref_setup() function, but passes it back to the caller.

Since the original intent seems to have been to split the work between
log_ref_setup and log_ref_write, make it the caller's responsibility
to allocate the buffer.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Reported-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>