spirv-tools: fix to use sdk-1.3.204 branch

spirv-tools: fix to use sdk-1.3.204 branch

Just as pointed out in a previous commit:
"""
We'll continue tagging the repos contributing with SDK releases, as
that is when all the testing of the various projects is performed
together.
"""

Now the repo has updated and the 'stable' branch is forcely overriden.
We need to use the 'sdk-1.3.204' branch.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>