This wasn't initialized for pre NV50 hardware.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reported-and-Tested-by: Mark Hounschell <markh@compro.net>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/series/84298/