Documentation: ABI: iio: Add missing newline at end of file

"git diff" says:

    \ No newline at end of file

after modifying the files.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio-dfsdm-adc-stm32

@@ -13,4 +13,4 @@ Description:
 			error on writing
 		If DFSDM input is SPI Slave:
 			Reading returns value previously set.
-			Writing value before starting conversions.
+			Writing value before starting conversions.
\ No newline at end of file