staging/lustre/obdecho: Better handle invalid create requests

When gettng an invalid create request in echo code (wrong group,
or no group at all), just return an error instead of crashing.

Signed-off-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>