Mac compile fix

mac.c

@@ -287,9 +287,9 @@ ScreenInit(int argc, char**argv)
 			   CGDisplayPixelsHigh(kCGDirectMainDisplay),
 			   bitsPerSample,
 			   CGDisplaySamplesPerPixel(kCGDirectMainDisplay),4);
-  rfbScreen->rfbServerFormat->redShift = bitsPerSample*2;
-  rfbScreen->rfbServerFormat->greenShift = bitsPerSample*1;
-  rfbScreen->rfbServerFormat->blueShift = 0;
+  rfbScreen->rfbServerFormat.redShift = bitsPerSample*2;
+  rfbScreen->rfbServerFormat.greenShift = bitsPerSample*1;
+  rfbScreen->rfbServerFormat.blueShift = 0;
 
   gethostname(rfbScreen->rfbThisHost, 255);
   rfbScreen->paddedWidthInBytes = CGDisplayBytesPerRow(kCGDirectMainDisplay);