bionic-amd64-tf-a-build: Use wget to download ARM Clang

There is an error to download ARM Clang with curl for the time being.
Use wget to download.

This change is similar to earlier change made for bionic-amd64-tf-m-build.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I4a269fab950ed9d0a76e7eb149137458127852d9
1 file changed