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>
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