iio: buffer: hw-consumer: free scan_mask on buffer release

In the Linux kernel, the following vulnerability has been resolved: iio: buffer: hw-consumer: free scan_mask on buffer release The scan_mask lifetime changed in commit 9a2e1233d38c ("iio: buffer: hw-consumer: remove redundant scan_mask flexible array"). Before that change, the scan mask storage was embedded in struct hw_consumer_buffer, so iio_hw_buf_release() could free the whole allocation with a single kfree(hw_buf). That commit moved the scan mask to a separate bitmap_zalloc() allocation stored in buffer.scan_mask, but left iio_hw_buf_release() unchanged. Free the scan mask in iio_hw_buf_release() before freeing the buffer wrapper.