ACPI: CPPC: Adjust return code for inline functions in !CONFIG_ACPI_CPPC_LIB

Checkpath emits the following warning:
```
WARNING: ENOTSUPP is not a SUSV4 error code, prefer EOPNOTSUPP
```

Adjust the code accordingly.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>