crash_reporter: add missing mkdir for crash_server rule

When doing a clean build, creating this file fails because the dir does
not yet exist:
echo "" > out/target/product/brilloemulator_arm/obj/ETC/crash_server_intermediates/crash_server
/bin/bash: out/target/product/brilloemulator_arm/obj/ETC/crash_server_intermediates/crash_server: No such file or directory

Bug: 24989289
Change-Id: If204dc0eb32e95ee66f97b568b4b9ae4050d3591