nfs: remove redundant call to nfs_context_set_write_error()

We don't need to call this in the direct, read, or pnfs resend paths and
the only other caller is the write path in nfs_page_async_flush() which
already checks and sets the pg_error on the context.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>