Fix silly typo in new builtin grep

The "-F" flag apparently got mis-translated due to some over-eager
copy-paste work into a duplicate "-H" when using the external grep.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

builtin-grep.c

@@ -455,7 +455,7 @@ static int external_grep(struct grep_opt *opt, const char **paths, int cached)
 	push_arg("grep");
 	push_arg("-H");
 	if (opt->fixed)
-		push_arg("-H");
+		push_arg("-F");
 	if (opt->linenum)
 		push_arg("-n");
 	if (opt->regflags & REG_EXTENDED)