i2c: stm32f7: fix documentation typo

Some data structure members were either misspelled or missing.

Fixes: aeb068c5 ("i2c: i2c-stm32f7: add driver")
Fixes: 380b8a85e7 ("i2c: i2c-stm32f7: Add initial SMBus protocols support")
Signed-off-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>