Always call SetMode in soong_zip

In addition to setting the mode, SetMode also marks the file
as created by Unix, which seems to cause Debian's unzip tool
to handle UTF-8 filenames correctly.

Fixes: 184575223
Test: TestZip
Change-Id: I0e839dc3d27aaa9abced0eb1d3c4c0f8eed3e3c4