reflog: use parse_config_key in config callback

This doesn't save any lines, but does keep us from doing
error-prone pointer arithmetic with constants.

Signed-off-by: Jeff King <peff@peff.net>
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/reflog.c

@@ -510,26 +510,27 @@ static int parse_expire_cfg_value(const char *var, const char *value, unsigned l
 
 static int reflog_expire_config(const char *var, const char *value, void *cb)
 {
-	const char *lastdot = strrchr(var, '.');
+	const char *pattern, *key;
+	int pattern_len;
 	unsigned long expire;
 	int slot;
 	struct reflog_expire_cfg *ent;
 
-	if (!lastdot || prefixcmp(var, "gc."))
+	if (parse_config_key(var, "gc", &pattern, &pattern_len, &key) < 0)
 		return git_default_config(var, value, cb);
 
-	if (!strcmp(lastdot, ".reflogexpire")) {
+	if (!strcmp(key, "reflogexpire")) {
 		slot = EXPIRE_TOTAL;
 		if (parse_expire_cfg_value(var, value, &expire))
 			return -1;
-	} else if (!strcmp(lastdot, ".reflogexpireunreachable")) {
+	} else if (!strcmp(key, "reflogexpireunreachable")) {
 		slot = EXPIRE_UNREACH;
 		if (parse_expire_cfg_value(var, value, &expire))
 			return -1;
 	} else
 		return git_default_config(var, value, cb);
 
-	if (lastdot == var + 2) {
+	if (!pattern) {
 		switch (slot) {
 		case EXPIRE_TOTAL:
 			default_reflog_expire = expire;
@@ -541,7 +542,7 @@ static int reflog_expire_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 
-	ent = find_cfg_ent(var + 3, lastdot - (var+3));
+	ent = find_cfg_ent(pattern, pattern_len);
 	if (!ent)
 		return -1;
 	switch (slot) {