cmd: undefined return value of do_extension_apply()

If 'extension apply all' is executed and no extension is found, the return
value of do_extension_apply() is undefined. Return CMD_RET_FAILURE in this
case.

Fixes: 2f84e9cf06d3 ("cmd: add support for a new "extension" command")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Kory Maincent <kory.maincent@bootlin.com>
diff --git a/cmd/extension_board.c b/cmd/extension_board.c
index bbb4812..f94abd6 100644
--- a/cmd/extension_board.c
+++ b/cmd/extension_board.c
@@ -111,6 +111,7 @@
 		return CMD_RET_USAGE;
 
 	if (strcmp(argv[1], "all") == 0) {
+		ret = CMD_RET_FAILURE;
 		list_for_each_entry(extension, &extension_list, list) {
 			ret = extension_apply(extension);
 			if (ret != CMD_RET_SUCCESS)