mmc: sunxi: Fix setup of last descriptor of dma transfer

The last descriptor might be the first descriptor as well, so use masking to
add the LD (last descriptor) bit and drop the DIC (disable interrupt on
completion) bit rather then hard assignment as hard assignment will override
the FD (first descriptor) bit if there is only 1 descriptor.

Also set the ER (end of ring) bit and clear buf_addr_ptr2 on the last
descriptor, like the android kernel code does.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: David Lanzendörfer <david.lanzendoerfer@o2s.ch>
Reported-by:  <lixiang@allwinnertech.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>