lib: utils: json: Fix encoded_obj element size

The size of the JSON_TOK_ENCODED_OBJ type was not defined, which
caused errors when generating an array.

Signed-off-by: Robin-Charles Guihéneuf <robin-charles@hotmail.fr>

diff --git a/lib/utils/json.c b/lib/utils/json.c
index 19ccafd..e1b81ab 100644
--- a/lib/utils/json.c
+++ b/lib/utils/json.c
@@ -949,6 +949,7 @@
 	case JSON_TOK_OBJ_ARRAY:
 		return sizeof(struct json_obj_token);
 	case JSON_TOK_STRING:
+	case JSON_TOK_ENCODED_OBJ:
 		return sizeof(char *);
 	case JSON_TOK_INT:
 	case JSON_TOK_UINT: