comedi: remove unused helper function dma_chain_flag_bits

comedi: remove unused helper function dma_chain_flag_bits

The helper function dma_chain_flag_bits is not being called from
anywhere, it is redundant and can be removed.

Cleans up clang scan build warning:
drivers/comedi/drivers/cb_pcidas64.c:377:28: warning: unused
function 'dma_chain_flag_bits' [-Wunused-function]

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20240308131848.2057693-1-colin.i.king@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>