aco: Initialize ds_state.front.writeMask.

Fix defect reported by Coverity Scan.

Uninitialized scalar variable (UNINIT) uninit_use: Using uninitialized value ds_state.front. Field ds_state.front.writeMask is uninitialized.

Fixes: d488d0fd ("aco: add framework for testing isel and integration tests") Signed-off-by: Vinson Lee vlee@freedesktop.org