cpufreq: ACPI: Simplify MSR read on the boot CPU

Replace the 32-bit MSR access function with a 64-bit variant to simplify
the call site, eliminating unnecessary 32-bit value manipulations.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Link: https://patch.msgid.link/20241106182313.165297-1-chang.seok.bae@intel.com


[ rjw: Subject edit ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>