drivers/acpi: Remove function cast

Remove the function cast in the ACPI_DECLARE_PROBE_ENTRY macro to ensure
that the functions passed as a last parameter to this macro have the
right prototype.

This is an effort to enable -Wcast-function-type in the top-level Makefile
to support Control Flow Integrity builds.

Suggested-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Oscar Carter <oscar.carter@gmx.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lore.kernel.org/r/20200530143430.5203-4-oscar.carter@gmx.com