hexagon: update reference, kerneltrap.org no longer works

kerneltrap.org no longer works, update to a working reference

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Acked-by: Richard Kuo <rkuo@codeaurora.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>