iio:dummy: Drop set but unused variable len.

Not sure what the thinking was here, as lost to history, but the
variable is clearly not used so get rid of it.

Warning seen with clang W=1 tests (may be present with other compilers
and build options).
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20211128172445.2616166-11-jic23@kernel.org

drivers/iio/dummy/iio_simple_dummy_buffer.c

@@ -45,7 +45,6 @@ static irqreturn_t iio_simple_dummy_trigger_h(int irq, void *p)
 {
 	struct iio_poll_func *pf = p;
 	struct iio_dev *indio_dev = pf->indio_dev;
-	int len = 0;
 	u16 *data;
 
 	data = kmalloc(indio_dev->scan_bytes, GFP_KERNEL);
@@ -79,7 +78,6 @@ static irqreturn_t iio_simple_dummy_trigger_h(int irq, void *p)
 					  indio_dev->masklength, j);
 			/* random access read from the 'device' */
 			data[i] = fakedata[j];
-			len += 2;
 		}
 	}