staging: lustre: libcfs: repair improper unlikely test

The scripts to replace NULL test got confused with the
macro parenthesis so the unlikely test in libcfs_private.h
ended up incorrect. This fixes this error.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>