ACPI / PCC: Use pr_debug() for debug messages in pcc_init()

pcc_init() uses pr_err() to print two messages that are really debug
and not interesting to users.  Replace those pr_err() with pr_debug().

Reported-by: Cristian <caravena@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>