dma: fix ipu_idmac.c to not discard the last queued buffer

This also fixes the case of a single queued buffer, for example, when taking a
single frame snapshot with the mx3_camera driver.

Reported-by: Agustin Ferrin Pozuelo <gatoguan-os@yahoo.com>
Tested-by: Agustin Ferrin Pozuelo <gatoguan-os@yahoo.com>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>