NFSv4.2: Protect copy offload and clone against 'eof page pollution'

The NFSv4.2 copy offload and clone functions can also end up extending
the size of the destination file, so they too need to call
nfs_truncate_last_folio().

Reported-by: Olga Kornievskaia <okorniev@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>