staging/lustre/osc: Fix reverted condition in osc_lock_weight

When imprting clio simplification patch, the check for
pbject got reversed by mistake when converting from
if (obj == NULL) it somehow became (if (obj) which is obviously wrong,
and so when it does hit, a crash was happening as result.

Fix the condition and all if fine now.

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