Fix git {log,show,...} --pretty=email

An earlier --subject-prefix patch forgot that format-patch is
not the only codepath that adds the "[PATCH]" prefix, and broke
everybody else in the log family.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

builtin-log.c

@@ -435,7 +435,6 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	rev.ignore_merges = 1;
 	rev.diffopt.msg_sep = "";
 	rev.diffopt.recursive = 1;
-	rev.subject_prefix = "PATCH";
 
 	rev.extra_headers = extra_headers;
 

revision.c

@@ -567,6 +567,7 @@ void init_revisions(struct rev_info *revs, const char *prefix)
 	revs->min_age = -1;
 	revs->skip_count = -1;
 	revs->max_count = -1;
+	revs->subject_prefix = "PATCH";
 
 	revs->prune_fn = NULL;
 	revs->prune_data = NULL;