arm: dma-mapping.c: Change the dma length in sg lists

Currently on 32-bit, the sg lists are virtually contiguous, but the dma
length of tail entries are not reorganized into zero, then error will
happen in ion_sgl_sync_range() which will check the sg lists and warn
if the dma length of tail entries is not zero.This warning is designed
for 64-bit. So change the 32-bit reorganization of sg lists like 64-bit.

Change-Id: I82e3832f8607df88ff832ece67d5dfa2791de51e
Signed-off-by: Qingqing Zhou <qqzhou@codeaurora.org>