glsl: initialise killed_all field.

coverity pointed out this field was being used uninitialised.

Note: This is a candidate for stable branches.

Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/glsl/opt_constant_propagation.cpp

@@ -92,6 +92,7 @@ public:
    ir_constant_propagation_visitor()
    {
       progress = false;
+      killed_all = false;
       mem_ctx = ralloc_context(0);
       this->acp = new(mem_ctx) exec_list;
       this->kills = new(mem_ctx) exec_list;