gpu: ion: Add missing argument to iommu map func

There exists one definition for ion_map_iommu
function when ION is enabled and one definition when
ION is disabled. The argument list for the definition used
when ION is disabled is missing the buffer_size argument causing
compilation error for targets that call this function without
ION enabled.

Add buffer_size argument to ion_map_iommu function
for targets that does not have ION enabled.

Change-Id: Ie184e4a6dbec2bc3dff75ab3b25985fd64e2baac
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>