staging: comedi: me_daq: tidy up control 1 register defines

Rename the bits of this register so they have association with the
register. Use the BIT macro to define the bits.

Add a macro to select the ADC mode and remove the magic value used
to stop conversion.

Reading the control 1 register starts an analog input conversion.
For aesthetics, remove the MC_ADC_START define and just use the
ME_CTRL1_REG define to read the register.

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>