i2c: mediatek: Fix wrong dma sync flag

The right flag is apdma_sync when apdma remove hand-shake signel.

Fixes: 05f6f727 ("i2c: mediatek: Fix apdma and i2c hand-shake timeout")
Signed-off-by: Qii Wang <qii.wang@mediatek.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>