staging/iio: IIO_SIMPLE_DUMMY_BUFFER neds IIO_BUFFER

An obviously missing 'select' statement, without this we
get a link error
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: linux-iio@vger.kernel.org
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/staging/iio/Kconfig

@@ -37,6 +37,7 @@ config IIO_SIMPLE_DUMMY_EVENTS
 
 config IIO_SIMPLE_DUMMY_BUFFER
 	boolean "Buffered capture support"
+	select IIO_BUFFER
 	select IIO_KFIFO_BUF
 	help
 	  Add buffered data capture to the simple dummy driver.