staging: comedi: adl_pci9118: introduce pci9118_timer_set_mode()

This driver uses 32-bit instructions to write the 8254 timers so we
can't use the helper functions provided by 8253.h.

To clarify the code introduce a helper function to set the timer mode.

Remove the unnecessary commented out timer mode programming.

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>