rsi: return explicit error values

Explicitly return constants instead of variable (and rely on
it to be explicitly initialized), if the value is supposed
to be fixed anyways. Align it with the rest of the driver,
which does it the same way.

Signed-off-by: Enrico Weigelt <info@metux.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>