staging: lustre: obdclass: return -EFAULT if copy_from_user() fails

The copy_from_user() function returns the number of bytes which we
weren't able to copy.  We don't want to return that to the user but
instead we want to return -EFAULT.

Fixes: d7e09d03 ("staging: add Lustre file system client support")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>