platform/x86: intel_pmc_ipc: Apply same width for offset definitions

Apply same width for offset definitions to make code more consistent.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>