u-boot.mk: use openwrt url instead of lede project

The LEDE URL is automatically redirected to the OpenWRT one,
returning an HTTP 301 code (Moved Permanently).

Also, use https, as indicated by the redirect.

Signed-off-by: Luis Araneda <luaraneda@gmail.com>

include/u-boot.mk

@@ -3,7 +3,7 @@ PKG_NAME ?= u-boot
 ifndef PKG_SOURCE_PROTO
 PKG_SOURCE = $(PKG_NAME)-$(PKG_VERSION).tar.bz2
 PKG_SOURCE_URL = \
-	http://sources.lede-project.org \
+	https://sources.openwrt.org \
 	ftp://ftp.denx.de/pub/u-boot
 endif