x86/rtc: Simplify PNP ids check

compare_pnp_id() already iterates over the single linked pnp_ids list
starting with the id past to it.

So there is no need for add_rtc_cmos() to call compare_pnp_id()
for each id on the list.

No change in functionality intended.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: linux-kernel@vger.kernel.org