drm/radeon: convert radeon vfct code to use acpi_get_table_with_size

commit 7c3906d04a4587dceaa78cc1ae6b14e6454ee02a upstream.

Allows us to verify the table size.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>