staging: comedi: addi_apci_3120: fix counter and external interrupt disable

The APCI3120_DISABLE_ALL_TIMER define define is not needed, and it's used
incorrectly in apci3120_cancel(). The define is a mask of the bits needed
to disable the counters. Writing the value directly sets unintended bits.

Prior to writing the value, the 'devpriv->us_OutputRegister' is set to 0
and written to the register. This disables all the timers and the external
trigger.

Remove the unnecessary apci3120_exttrig_disable() call as well as the write
of APCI3120_DISABLE_ALL_TIMER.

In apci3120_interrupt(), remove the unnecessary mask and write to disable
all the timers. The COMEDI_CB_EOA event will cause the core to call the
(*cancel) operation which will disable the timers.

Remove the unused define.

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>