i2c: stm32f7: fix & reorder remove & probe error handling

Add missing dma channels free calls in case of error during probe
and reorder the remove function so that dma channels are freed after
the i2c adapter is deleted.
Overall, reorder the remove function so that probe error handling order
and remove function order are same.

Fixes: 7ecc8cfd ("i2c: i2c-stm32f7: Add DMA support")
Signed-off-by: Alain Volmat <alain.volmat@st.com>
Reviewed-by: Pierre-Yves MORDRET <pierre-yves.mordret@st.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>