Staging: comedi: change pr_err to dev_err in __unioxx5_digital_write

This is a patch which subsitutes pr_err with the preferred dev_err
for device drivers in __unioxx5_digital_write.

The function definition of __unioxx5_digital_write has been changed
to take the pointer to the struct comedi_subdevice as a parameter
instead of the pointer to struct unioxx5_subd_priv.

The pointers to the stuct device and the struct unioxx5_subd_priv are
obtained through the pointer to the struct comedi_subdevice in this
function.

The function call to __unioxx5_digital_write in unioxx5_subdev_write
has been changed to pass the pointer to the struct comedi_subdevice

Signed-off-by: Conrad Gomes <conrad.s.j.gomes@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>