drm/nouveau/kms/nv50-: Don't call HEAD_SET_CRC_CONTROL in head907d_mode()

This was a mistake that was present before, but never got noticed until
we converted over to using nvidia's class headers for display
programming. Luckily though it never caused any problems, since we
always end up calling crc907d_set_src() after head907d_mode().

So, let's get rid of this.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>