msm: ipa: fix division by 0 for DMA pipes

For DMA pipes, bufer size is 0. This commit fixes a
division by 0 in kernel when connecting DMA pipes.

Change-Id: I11551594e5115e71aa116cc7238953205a4118c3
CRs-Fixed: 1085266
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Skylar Chang <chiaweic@codeaurora.org>