media: iris: Add buffer to list only after successful allocation

In the Linux kernel, the following vulnerability has been resolved: media: iris: Add buffer to list only after successful allocation Move `list_add_tail()` to after `dma_alloc_attrs()` succeeds when creating internal buffers. Previously, the buffer was enqueued in `buffers->list` before the DMA allocation. If the allocation failed, the function returned `-ENOMEM` while leaving a partially initialized buffer in the list, which could lead to inconsistent state and potential leaks. By adding the buffer to the list only after `dma_alloc_attrs()` succeeds, we ensure the list contains only valid, fully initialized buffers.