staging: comedi: ni_mio_common: absorb helpers into ni_freq_out_insn_config()

Absorb the helper functions that handle the INSN_CONFIG_SET_CLOCK_SRC and
INSN_CONFIG_GET_CLOCK_SRC comedi instructions.

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>