msm: camera: isp: fix integer overflow

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: Ia9e2e3ae2fc1ec5933ccea5390ffd3ccb997976d
Signed-off-by: Petar Sivenov <psiven@codeaurora.org>