arm64: dts: qcom: pm8941-rtc add alarm register

A few descriptions including a qcom,pm8941-rtc describe two reg-names
for the "rtc" and "alarm" register banks, but only one offset.
For consistency with reg-names, add the "alarm" register offset.
No functional change is expected from this.

Signed-off-by: Eric Chanudet <echanude@redhat.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Tested-by: Andrew Halaney <ahalaney@redhat.com> # sa8540p-ride
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221219191000.2570545-5-echanude@redhat.com