ceph: call netfs_subreq_terminated with was_async == false

"was_async" is a bit misleadingly named. It's supposed to indicate
whether it's safe to call blocking operations from the context you're
calling it from, but it sounds like it's asking whether this was done
via async operation. For ceph, this it's always called from kernel
thread context so it should be safe to set this to false.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>