nouveau/dmem: fix copy-paste error in nouveau_dmem_migrate_chunk()

Fix call to nouveau_fence_emit() with wrong channel parameter.

Fixes: 7f2a0b50 ("drm/nouveau: fence: separate fence alloc and emit")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230807163238.2091-2-dakr@redhat.com