rust: do not copy the SysBusDevice

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

rust/hw/core/src/sysbus.rs

@@ -78,7 +78,7 @@ where
         assert!(bql::is_locked());
         // SAFETY: the BQL ensures that no one else writes to sbd.mmio[], and
         // the SysBusDevice must be initialized to get an IsA<SysBusDevice>.
-        let sbd = unsafe { *self.upcast().as_ptr() };
+        let sbd = unsafe { &*self.upcast().as_ptr() };
         let id: usize = id.try_into().unwrap();
         if sbd.mmio[id].memory.is_null() {
             None