iio: drop wrong reference from Kconfig

The documentation lives in drivers/staging/iio/Documentation, but
according to Jonathan it's obsolete and needs fixing.
Signed-off-by: NJiri Kosina <jkosina@suse.cz>
Acked-by: NJonathan Cameron <jic23@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/iio/Kconfig

@@ -8,8 +8,7 @@ menuconfig IIO
 	help
 	  The industrial I/O subsystem provides a unified framework for
 	  drivers for many different types of embedded sensors using a
-	  number of different physical interfaces (i2c, spi, etc). See
-	  Documentation/iio for more information.
+	  number of different physical interfaces (i2c, spi, etc).
 
 if IIO