Properly reference operator.

This wasn't actually Doxygen's fault.

src/Magnum/Resource.h

@@ -201,10 +201,10 @@ class Resource {
         #ifdef MAGNUM_BUILD_DEPRECATED
         /**
          * @overload
-         * @deprecated Use the explicit @ref operator*() or operator->()
-         *      instead. Implicit conversion is no longer allowed if it might
-         *      throw an assertion.
-         * @todoc Explicit reference when Doxygen can handle operator->()
+         * @deprecated Use the explicit @ref Magnum::Resource::operator*() "operator*()"
+         *      or @ref Magnum::Resource::operator->() "operator->()" instead.
+         *      Implicit conversion is no longer allowed if it might throw an
+         *      assertion.
          */
         CORRADE_DEPRECATED("use operator*() or operator->() instead") operator U&() { return **this; }
         #endif