iio: buffer: hw-consumer: fix use-after-free in error path

In the Linux kernel, the following vulnerability has been resolved:

iio: buffer: hw-consumer: fix use-after-free in error path

In the err_put_buffers cleanup path of iio_hw_consumer_alloc(), the code

was using list_for_each_entry() to iterate through buffers while calling

iio_buffer_put() which can free the current buffer if refcount drops to 0.

The list_for_each_entry() loop macro then evaluates buf->head.next to

continue iteration, accessing the freed buffer.

Fix this by using list_for_each_entry_safe().