i2c: mediatek: Reset the handshake signal between i2c and dma

Due to changes in the hardware design of the handshaking signal
between i2c and dma, it is necessary to reset the handshaking
signal before each transfer to ensure that the multi-msgs can
be transferred correctly.

Signed-off-by: Kewei Xu <kewei.xu@mediatek.com>
Reviewed-by: Qii Wang <qii.wang@mediatek.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>