i2c: mediatek: Reset DMA engine in hardware init function

Reset DMA in hardware init function to avoid unknown hardware state
before do any I2C operation.

Signed-off-by: Liguo Zhang <liguo.zhang@mediatek.com>
Signed-off-by: Eddie Huang <eddie.huang@mediatek.com>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>