nfs: pass on count for CLONE operations

Currently we pass uninitialized stack garbage in the count parameter.
The value is usually large enought to clone whole files and thus let
simple tests pass, but it makes the tests for range clones very unhappy.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>