ARM: dts: armada388-clearfog: increase speed of i2c0 to 400kHz

All the devices on I2C0 support fast mode, so increase the bus speed
to match.  The Armada 388 is known to have a timing issue when in
standard mode, which we believe causes the ficticious device at 0x64
to appear.

[gregory.clement@bootlin.com: Note that since the commit fbffee74
("ARM: dts: Fix I2C repeated start issue on Armada-38x") in 4.14, the
timing issue is managed for the Armada 38x SoCs.]

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>