TF-A: revert to use semicolon separator in the RUN command

revert https://review.trustedfirmware.org/c/ci/dockerfiles/+/6672
It was working as expected, as long as we keep "set -e" in the RUN
command. We want to limit RUN commands as much possible to reduce the
number of layers.

Signed-off-by: Fathi Boudra <fathi.boudra@linaro.org>
Change-Id: I78a687c24c0fb53ce252a441837b8e4df1076b5d
1 file changed