trusted-firmware-a.mk: fix release download URL
The URL of trusted-firmware-a is no longer available for
downloading release:
https://git.trustedfirmware.org/TF-A/trusted-firmware-a.git/
curl: (22) The requested URL returned error: 401 Unauthorized
So we switch to the GitHub mirror repository to download.
Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>
Link: https://github.com/openwrt/openwrt/pull/17360
Signed-off-by: Robert Marko <robimarko@gmail.com>
(cherry picked from commit
4b6eb631e18b3ccccada91d5bccbb684e6ccc5a4)