boot: superfluous assignment in bootflow_menu_new()

ret is assigned a value 0 which is never used but
is immediately overwritten in the next statement.

Addresses-Coverity-ID: 453304 ("Unused value")
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

boot/bootflow_menu.c

@@ -120,7 +120,6 @@ int bootflow_menu_new(struct expo **expp)
 
 		if (ret < 0)
 			return log_msg_ret("itm", -EINVAL);
-		ret = 0;
 		priv->num_bootflows++;
 	}