staging/lustre/clio: Do not allow group locks with gid 0

When a group lock with GID=0 is released (put_grouplock is
called), an assertion in cl_put_grouplock is hit.

We should not allow group lock requests with GID=0, instead
we should return -EINVAL.

Signed-off-by: Patrick Farrell <paf@cray.com>
Reviewed-on: http://review.whamcloud.com/12459
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5817


Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: frank zago <fzago@cray.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>