nv50/ir: Initialize Value member id in constructor.

Fix defect reported by Coverity Scan.

Uninitialized scalar field (UNINIT_CTOR)
uninit_member: Non-static class member id is not initialized in
this constructor nor in any functions that it calls.

Suggested-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10401>

src/gallium/drivers/nouveau/codegen/nv50_ir.cpp

@@ -214,7 +214,7 @@ ValueDef::replace(const ValueRef &repVal, bool doSet)
       set(repVal.get());
 }
 
-Value::Value()
+Value::Value() : id(-1)
 {
   join = this;
   memset(&reg, 0, sizeof(reg));