drm/nouveau/fifo/ga102: initialise chid on return from channel creation

drm/nouveau/fifo/ga102: initialise chid on return from channel creation

Turns out caller isn't zero-initialised after-all.

Fixes: 2afd00829b4d ("drm/nouveau/ga102-: support ttm buffer moves via copy engine")
Reported-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210921090735.247236-1-skeggsb@gmail.com
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>