anv: don't report error with other vendor DRM devices

anv: don't report error with other vendor DRM devices

Enumeration should just skip unsupported DRM devices.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 34c8621c3b37 ("anv: Allow enumerating multiple physical devices")
Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2386
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3481>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3481>