staging: android: ion: Set the length of the DMA sg entries in buffer

ion_buffer_create() will allocate a buffer and then create a DMA
mapping for it, but it forgot to set the length of the page entries.

Signed-off-by: Liviu Dudau <Liviu.Dudau@arm.com>
Signed-off-by: Jon Medhurst <tixy@linaro.org>
Acked-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>