staging: olpc_dcon: Replace flush_scheduled_work() with flush_work().

Since "struct dcon_priv" is per a device struct, I assume that
dcon_set_source_sync() needs to wait for only one work associated with
that device. Therefore, wait for only that work using flush_work().

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: https://lore.kernel.org/r/a973969d-cfd0-adc8-2651-d299199dbd7b@I-love.SAKURA.ne.jp


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>