staging: comedi: amplc_pci224: convert CLK_CONFIG() macro to function

Convert the `CLK_CLKFIG(chan, src)` macro to a static function
`pci224_clk_config(chan, src)`.  This is consistent with an earlier
change to convert `GAT_CONFIG(chan, src)` to a static function.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>