drm/nouveau: pass drm to nv50_dmac_create(), rather than device+disp

Both of these are stored in nouveau_drm already.

Signed-off-by: Ben Skeggs <bskeggs@nvidia.com>
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240726043828.58966-31-bskeggs@nvidia.com