Fix DIFF_QUEUE_CLEAR refactoring

It introduced a macro to reduce repeated assignments to three fields,
but an unrelated and incorrect change snuck in by mistake, which broke
commands like "git diff-files -p --submodule".

Noticed by Sven Verdoolaege.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff.c

@@ -2540,7 +2540,6 @@ static void run_checkdiff(struct diff_filepair *p, struct diff_options *o)
 void diff_setup(struct diff_options *options)
 {
 	memset(options, 0, sizeof(*options));
-	memset(&diff_queued_diff, 0, sizeof(diff_queued_diff));
 
 	options->file = stdout;