staging: android: ion: Get rid of map_dma/unmap_dma

The map_dma API interface was designed to generate an sg_table.
Currently, every client just creates the table at allocation time and
then returns the one table. Nothing happens on unmap_dma either.
Just get rid of the API and assign the sg_table directly.

Signed-off-by: Laura Abbott <labbott@redhat.com>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>