rfb: Fix hidden function overload warnings

rfb: Fix hidden function overload warnings

Fix the following warnings emitted by Clang:

/home/shade/dev/tigervnc/common/rfb/Configuration.h:164:18: note: hidden overloaded virtual function 'rfb::VoidParameter::setParam' declared here: different number of parameters (0 vs 1)
    virtual bool setParam();
                 ^
/home/shade/dev/tigervnc/common/rfb/Configuration.h:256:18: error: 'rfb::BinaryParameter::setParam' hides overloaded virtual function [-Werror,-Woverloaded-virtual]
    virtual void setParam(const void* v, int l);
                 ^
/home/shade/dev/tigervnc/common/rfb/Configuration.h:164:18: note: hidden overloaded virtual function 'rfb::VoidParameter::setParam' declared here: different number of parameters (0 vs 2)
    virtual bool setParam();