Here's another doublescan fix for atyfb.

Previosly var<->crtc conversion would do different things depending on 
which way the conversion was made. 
var->crtc: vdisp = ((yres-1)<<1) 
crtc->var: yres  = ((vdisp+1)>>1)

That's obviously wrong. And thus fbset would report incorrect yres value. 
The patch changes var->crtc conversion to do vdisp = ((yres<<1)-1).

I'm not entirely sure which way is the right way but at least now things 
work as expected.

-- 
Ville Syrjälä
syrjala@sci.fi
http://www.sci.fi/~syrjala/