macosx: resize the retina bitmaps for the progressions knobs so AppKit doesn't do stupid things

This prevents the knob to be blurred in the bright interface style because the retina bitmap wasn't twice as large as the regular one
(cherry picked from commit 748e7339cd025dbf0d297a16cb9ea2a029e7db61)

modules/gui/macosx/misc.m

@@ -546,8 +546,7 @@ void _drawFrameInRect(NSRect frameRect)
     [[NSGraphicsContext currentContext] restoreGraphicsState];
 
     NSRect knobRect = [[self cell] knobRectFlipped:NO];
-    if (b_dark)
-        knobRect.origin.y+=2;
+    knobRect.origin.y+=1;
     [self drawKnobInRect: knobRect];
 }