s4:dsdb_notification: fix the --picky-developer build with gcc 4.4.3

s4:dsdb_notification: fix the --picky-developer build with gcc 4.4.3

The following warning/error is reported:

[1891/4034] Compiling source4/dsdb/samdb/ldb_modules/dsdb_notification.c
cc1: warnings being treated as errors
../source4/dsdb/samdb/ldb_modules/dsdb_notification.c: In function 'dsdb_notification_filter_search':
../source4/dsdb/samdb/ldb_modules/dsdb_notification.c:192: error: value computed is not used
Waf: Leaving directory `/memdisk/autobuild/fl/b300949/samba/bin'
Build failed:  -> task failed (err #1):
	{task: cc dsdb_notification.c -> dsdb_notification_84.o}

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>