staging: comedi: ni_labpc: cleanup labpc_counter_load() usage

For aesthetic reasons, move the labpc_counter_load() function so
it's by the labpc_counter_set_mode() function.

Update all the labpc_counter_load() calls so that the I8254_MODE*
enums are used instead of the open coded values.

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