[PATCH] atyfb, rivafb: minor fixes

aty128fb: return an error in the unlikely event that we cannot calculate
some key PLL info

rivafb:
* call CalcStateExt() directly, rather than via function pointers, since
  CalcStateExt() is the only value ever assigned to ->CalcStateExt().
* propagate error return back from CalcVClock() through callers

Signed-off-by: Jeff Garzik <jeff@garzik.org>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>