i2c: mediatek: Send i2c master code at more than 1MHz

The master code needs to being sent when the speed is more than
I2C_MAX_FAST_MODE_PLUS_FREQ, not I2C_MAX_FAST_MODE_FREQ in the
latest I2C-bus specification and user manual.

Signed-off-by: Qii Wang <qii.wang@mediatek.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>