msm: camera: isp: Fix integer overflow in vfe 46

An intermediate calculation for size of AXI UB buffers results in
32bit overflow. This patch adds a 64bit calculation for temporary
result to avoid the overflow.

Change-Id: I3851437d91e6bf02c99d60d1f8eacf7e9d3b0489
Signed-off-by: Senthil <skrajago@codeaurora.org>