spi: docs: spidev: fix echo command format

The two example echo commands for binding the spidev driver were being
rendered as one line in the HTML output. This patch makes use of the
restructured text :: to format the commands as a code block instead
which preserves the line break.
Signed-off-by: David Lechner <dlechner@baylibre.com>
Link: https://msgid.link/r/20240319183344.2106335-1-dlechner@baylibre.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/spi/spidev.rst

@@ -61,7 +61,7 @@ the spidev driver failing to probe.
 
 Sysfs also supports userspace driven binding/unbinding of drivers to
 devices that do not bind automatically using one of the tables above.
-To make the spidev driver bind to such a device, use the following:
+To make the spidev driver bind to such a device, use the following::
 
     echo spidev > /sys/bus/spi/devices/spiB.C/driver_override
     echo spiB.C > /sys/bus/spi/drivers/spidev/bind