drm: report consistent errors when checking syncobj capibility

We've been somewhat inconsistent when adding the new ioctl and
returned ENODEV instead of EOPNOTSUPPORTED upon failing the syncobj
capibility.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: ea569910 ("drm/syncobj: add transition iotcls between binary and timeline v2")
Fixes: 01d6c357 ("drm/syncobj: add support for timeline point wait v8")
Cc: Dave Airlie <airlied@redhat.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Chunming Zhou <david1.zhou@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com> for the series.
Reviewed-by: Chunming Zhou <david1.zhou@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190416123048.2913-1-lionel.g.landwerlin@intel.com