lockd: fix failure to cleanup client locks

In my testing, we're sometimes hitting the request->fl_flags & FL_EXISTS
case in posix_lock_inode, presumably just by random luck since we're not
actually initializing fl_flags here.

This probably didn't matter before commit 7f024fcd ("Keep read and
write fds with each nlm_file") since we wouldn't previously unlock
unless we knew there were locks.

But now it causes lockd to give up on removing more locks.

We could just initialize fl_flags, but really it seems dubious to be
calling vfs_lock_file with random values in some of the fields.

Fixes: 7f024fcd ("Keep read and write fds with each nlm_file")
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
[ cel: fixed checkpatch.pl nit ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>