Add missing break in lock_partialfilelock(..) with NFS_RESERR

This will help ensure that the right error is trickled up when the
function is called if the lock status is NFS_RESERR

Differential Revision: https://reviews.freebsd.org/D6622
Reviewed by: rmacklem
Approved by: re (gjb)
Tested with: fsx; svn info/svnversion (uses bdb locking); locktests from Bull http://nfsv4.bullopensource.org/tools/tests/locktest.php
MFC after: 2 weeks
Reported by: Coverity
CID: 1008161, 1304956
Sponsored by: EMC / Isilon Storage Division