iio: accel: sca3000: memory corruption in sca3000_read_first_n_hw_rb()

commit eda7d0f3 upstream.

"num_read" is in byte units but we are write u16s so we end up write
twice as much as intended.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/staging/iio/accel/sca3000_ring.c

@@ -116,7 +116,7 @@ static int sca3000_read_first_n_hw_rb(struct iio_buffer *r,
 	if (ret)
 		goto error_ret;
 
-	for (i = 0; i < num_read; i++)
+	for (i = 0; i < num_read / sizeof(u16); i++)
 		*(((u16 *)rx) + i) = be16_to_cpup((u16 *)rx + i);
 
 	if (copy_to_user(buf, rx, num_read))