bugfix: add virtual destructor to zoneinterface

ZoneInterface is a virtual abstract class and needs a virtual
destructor.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I4159a88327d04bc344e484263f4c1d2875d81713
diff --git a/ipmi/control.hpp b/ipmi/control.hpp
index 1cd1612..4f1f0ad 100644
--- a/ipmi/control.hpp
+++ b/ipmi/control.hpp
@@ -12,6 +12,8 @@
 class ZoneControlInterface
 {
   public:
+    virtual ~ZoneControlInterface() = default;
+
     // Reads the fan control property (either manual or failsafe) and returns an
     // IPMI code based on success or failure of this.
     virtual uint8_t getFanCtrlProperty(uint8_t zoneId, bool* value,