ACPI: processor: idle: Drop extra prefix from pr_notice()

Drop "ACPI: " from the pr_noitice() instance in
acpi_processor_cstate_first_run_checks(), because pr_fmt() causes
that prefix to be added to the message already.

Reported-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>