libkwineffects/glshader: set the correct maximum brightness

The maximum frame average brightness can be significantly lower than the actual
maximum brightness of the screen

src/libkwineffects/glshader.cpp

@@ -435,7 +435,7 @@ bool GLShader::setColorspaceUniforms(const ColorDescription &src, const ColorDes
         && setUniform(GLShader::IntUniform::SourceNamedTransferFunction, int(src.transferFunction()))
         && setUniform(GLShader::IntUniform::DestinationNamedTransferFunction, int(dst.transferFunction()))
         && setUniform(IntUniform::SdrBrightness, dst.sdrBrightness())
-        && setUniform(FloatUniform::MaxHdrBrightness, dst.maxFrameAverageBrightness());
+        && setUniform(FloatUniform::MaxHdrBrightness, dst.maxHdrHighlightBrightness());
 }
 
 bool GLShader::setColorspaceUniformsFromSRGB(const ColorDescription &dst)