rv/rtapp/wakeup: Use "rv_this" the rv_monitor variable

Commit d9e4c61a12dd ("rv: Use generic rv_this for the rv_monitor
variable in LTL") renamed the rv_monitor variable to rv_this. But
rtapp/wakeup monitor was late to the party and missed that.

So for this monitor, rv_this is an empty struct. The reactor fails to
work, because rv_react() checks monitor->react and sees NULL.

Correct to "rv_this" and make the reactor work again.

Signed-off-by: Nam Cao <namcao@linutronix.de>
Fixes: d9e4c61a12dd ("rv: Use generic rv_this for the rv_monitor variable in LTL")
Link: https://lore.kernel.org/r/20261001044218.3508990-1-namcao@linutronix.de
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>