object-name: declare pointer type of extend_abbrev_len()'s 2nd parameter

Expose the expected type of the second parameter of extend_abbrev_len()
instead of casting a void pointer internally.  Just a single caller
passes in a void pointer, the rest pass the correct type.  Let the
compiler help keeping it that way.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: rscharfe

object-name.c

@@ -691,10 +691,9 @@ static inline char get_hex_char_from_oid(const struct object_id *oid,
 		return hex[oid->hash[pos >> 1] & 0xf];
 }
 
-static int extend_abbrev_len(const struct object_id *oid, void *cb_data)
+static int extend_abbrev_len(const struct object_id *oid,
+			     struct min_abbrev_data *mad)
 {
-	struct min_abbrev_data *mad = cb_data;
-
 	unsigned int i = mad->init_len;
 	while (mad->hex[i] && mad->hex[i] == get_hex_char_from_oid(oid, i))
 		i++;