staging: lustre: check length of char array

This fixes the following sparse error:

drivers/staging/lustre/lustre/obdclass/llog_ioctl.c:388:39: error: incompatible types for operation (>)
drivers/staging/lustre/lustre/obdclass/llog_ioctl.c:388:39:    left side has type char *ioc_inlbuf2
drivers/staging/lustre/lustre/obdclass/llog_ioctl.c:388:39:    right side has type int

Signed-off-by: Andreas Platschek <platschek@ict.tuwien.ac.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>