submodule--helper: fix a memory leak in print_status()

Fix a leak in print_status(), the compute_rev_name() function
implemented in this file will return a strbuf_detach()'d value, or
NULL.

This leak has existed since this code was added in
a9f8a37 (submodule: port submodule subcommand 'status' from shell
to C, 2017-10-06), but in 0b5e2ea (submodule--helper: don't print
null in 'submodule status', 2018-04-18) we added a "const"
intermediate variable for the return value, that "const" should be
removed.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Reviewed-by: Glen Choo <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

builtin/submodule--helper.c

@@ -583,10 +583,11 @@ static void print_status(unsigned int flags, char state, const char *path,
 	printf("%c%s %s", state, oid_to_hex(oid), displaypath);
 
 	if (state == ' ' || state == '+') {
-		const char *name = compute_rev_name(path, oid_to_hex(oid));
+		char *name = compute_rev_name(path, oid_to_hex(oid));
 
 		if (name)
 			printf(" (%s)", name);
+		free(name);
 	}
 
 	printf("\n");