Staging: comedi: change pr_err to dev_err in __unioxx5_analog_read

This is a patch which subsitutes pr_err with dev_err in
__unioxx5_analog_read as it is the preferred way to log in device
drivers

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>