NFS: use locks_copy_lock() to copy locks.

Using memcpy() to copy lock requests leaves the various
list_head in an inconsistent state.
As we will soon attach a list of conflicting request to
another pending request, we need these lists to be consistent.
So change NFS to use locks_init_lock/locks_copy_lock instead
of memcpy.

Signed-off-by: NeilBrown <neilb@suse.com>
Reviewed-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>