i2c: stm32f4: Mundane typo fix

s/postion/position/

Signed-off-by: Bhaskar Chowdhury <unixbhaskar@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Alain Volmat <alain.volmat@foss.st.com>
Reviewed-by: Pierre-Yves MORDRET <pierre-yves.mordret@foss.st.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>