locking/percpu-rwsem: Trigger contention tracepoints only if contended

We mistakenly always fire lock contention tracepoints in the writer path,
while it should be conditional on the trylock result.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Link: https://lore.kernel.org/r/20231108215322.2845536-1-namhyung@kernel.org