ni_release_ai_mite_channel(), ni_release_ao_mite_channel(),
ni_release_gpct_mite_channel() and ni_release_cdo_mite_channel()
call functions which interpret -1 as a special value meaning "no channel".
This patch adds explicit "no_channel" versions instead.

On the other hand, after "no_channel" versions are used,
ni_set_ai_dma_channel(), ni_set_ao_dma_channel(),
ni_set_gpct_dma_channel(), ni_set_cdo_dma_channel() are called with actual
"channel" parameter being always unsigned, so their signatures are changed
accordingly.

A side benefit of the changes is suppressesing 4 sparse warnings:
"warning: shift too big (4294967295) for type int".
Signed-off-by: Andrzej Pietrasiewicz <andrzejtp2010@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>