staging: xillybus: Reorganizing xilly_setupchannels()

Duplicate code in this function was moved into a new function,
xilly_get_dma_buffers().

There is no change in functionality.

Signed-off-by: Eli Billauer <eli.billauer@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>