media: stm32: dcmipp: correct error handling in dcmipp_create_subdevs

Correct error handling within the dcmipp_create_subdevs by properly
decrementing the i counter when releasing the subdevs.

Fixes: 28e0f377 ("media: stm32-dcmipp: STM32 DCMIPP camera interface driver")
Cc: stable@vger.kernel.org
Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
[hverkuil: correct the indices: it's [i], not [i - 1].]