staging: comedi: addi_apci_3120: tidy up devpriv->ctrl use

staging: comedi: addi_apci_3120: tidy up devpriv->ctrl use

The apci3120_setup_chan_list() function sets devpriv->ctrl to the scan length
(PR) and scan start (PA) values and writes the value to the register. There is
no need to mask the value first.

The apci3120_ai_insn_read() function calles apci3120_setup_chan_list(). There
is no need to clear devpriv->ctrl first or clear any additional bits and write
the register again. This also fixes an incorrect use of APCI3120_DISABLE_TIMER0
to disable the timer.

apci3120_cyclic_ai() also calls apci3120_setup_chan_list() so it does not need
to clear devpriv->ctrl or clear any addidional bits and write the register.

Update the comments in apci3120_reset() and apci3120_cancel().

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>