DT: binding: bcm2835-mbox: fix address typo in example

The address of the mailbox node in the example has a typo.
So fix it accordingly.
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Fixes: d4b5c782 ("dt/bindings: Add binding for the BCM2835 mailbox driver")
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Eric Anholt <eric@anholt.net>

Documentation/devicetree/bindings/mailbox/brcm,bcm2835-mbox.txt

@@ -12,7 +12,7 @@ Required properties:
 
 Example:
 
-mailbox: mailbox@7e00b800 {
+mailbox: mailbox@7e00b880 {
 	compatible = "brcm,bcm2835-mbox";
 	reg = <0x7e00b880 0x40>;
 	interrupts = <0 1>;