NFS: nfs_invalidate_folio() must observe the offset and size arguments

[ Upstream commit b7b85742 ]

If we're truncating part of the folio, then we need to write out the
data on the part that is not covered by the cancellation.

Fixes: d47992f8 ("mm: change invalidatepage prototype to accept length")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>