proper prototype for acpi_processor_tstate_has_changed()

This patch adds a proper prototype for acpi_processor_tstate_has_changed()
in include/acpi/processor.h

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Cc: Len Brown <lenb@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>