Distinguish between the case where dma information is not provided
within the DT and the case of an error during the dma init.
Exit the probe with error in case of an error during dma init.

Fixes: bb8822cb ("i2c: i2c-stm32: Add generic DMA API")
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>