rtc: cmos: Fix event handler registration ordering issue

In the Linux kernel, the following vulnerability has been resolved:

rtc: cmos: Fix event handler registration ordering issue

Because acpi_install_fixed_event_handler() enables the event

automatically on success, it is incorrect to call it before the

handler routine passed to it is ready to handle events.

Unfortunately, the rtc-cmos driver does exactly the incorrect thing

by calling cmos_wake_setup(), which passes rtc_handler() to

acpi_install_fixed_event_handler(), before cmos_do_probe(), because

rtc_handler() uses dev_get_drvdata() to get to the cmos object

pointer and the driver data pointer is only populated in

cmos_do_probe().

This leads to a NULL pointer dereference in rtc_handler() on boot

if the RTC fixed event happens to be active at the init time.

To address this issue, change the initialization ordering of the

driver so that cmos_wake_setup() is always called after a successful

cmos_do_probe() call.

While at it, change cmos_pnp_probe() to call cmos_do_probe() after

the initial if () statement used for computing the IRQ argument to

be passed to cmos_do_probe() which is cleaner than calling it in

each branch of that if () (local variable "irq" can be of type int,

because it is passed to that function as an argument of type int).

Note that commit 6492fed7d8c9 ("rtc: rtc-cmos: Do not check

ACPI_FADT_LOW_POWER_S0") caused this issue to affect a larger number

of systems, because previously it only affected systems with

ACPI_FADT_LOW_POWER_S0 set, but it is present regardless of that

commit.