ARM: dts: stm32: fix i2c node name on stm32f746 to prevent warnings

[ Upstream commit ad0ed10ba5792064fc3accbf8f0341152a57eecb ]

Replace upper case by lower case in i2c nodes name.

Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>