mailbox: pcc: Drop uninformative output during boot

When booting on an ACPI enabled system that does not provide the
Platform Communications Channel Table (PCCT), the pcc mailbox driver
prints -

[    0.484261] PCCT header not found.

during probe before returning -ENODEV.

This message clutters the bootlog and doesn't provide any useful
information. Drop this message.

Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Acked-by: Alexey Klimov <alexey.klimov@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>