[LR11x0] Added missing override

src/modules/LR11x0/LR11x0.h

@@ -824,7 +824,7 @@ class LR11x0: public PhysicalLayer {
       Overload with warm start enabled for PhysicalLayer compatibility.
       \returns \ref status_codes
     */
-    int16_t sleep();
+    int16_t sleep() override;
 
     /*!
       \brief Sets the module to sleep mode. To wake the device up, call standby().