i2c: meson: Use 50% duty cycle for I2C clock

The duty cycle of 33% is less than the required
by the I2C specs for the LOW period of the SCL
clock.

Move the duty cyle to 50% for 100Khz or lower
clocks, and (40% High SCL / 60% Low SCL) duty
cycle for clocks above 100Khz.

Signed-off-by: Lucas Tanure <tanure@linux.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>