staging: comedi: ni_mio_common: fix wrong insn_write handler

For counter subdevices, the `s->insn_write` handler is being set to the
wrong function, `ni_tio_insn_read()`.  It should be
`ni_tio_insn_write()`.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reported-by: Éric Piel <piel@delmic.com>
Fixes: 10f74377 ("staging: comedi: ni_tio: make ni_tio_winsn() a
  proper comedi (*insn_write)"
Cc: <stable@vger.kernel.org> # 3.17+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>