lock_rate_calc() error

- propagate errors back to upper level open routine

Signed-off-by: Jeff Garzik <jeff@garzik.org>
Cc: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
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