staging: comedi: amplc_pc236: remove dev_err() message due to allocation failure

The subdev_8255_init() call can only fail due to the allocation of the private
data. This failure will alreay have produced an error message. Remove the
redundant dev_err().

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>