clocksource/drivers/timer-ti-dm: Fix finding alwon timer

Clean-up commit b6999fa1c847 ("clocksource/drivers/timer-ti-dm: Use
of_address_to_resource()") caused a regression where pa is never set
making all related SoCs fail to boot. Let's fix this by setting pa
if found.

Fixes: b6999fa1c847 ("clocksource/drivers/timer-ti-dm: Use of_address_to_resource()")
Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230412064142.12726-1-tony@atomide.com