docs: dt: usage_model.rst: fix link for DT usage

The devicetree.org doesn't host the Device_Tree_Usage page
anymore. So, fix the link to point to a new address.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/usage-model.rst

@@ -12,7 +12,7 @@ This article describes how Linux uses the device tree.  An overview of
 the device tree data format can be found on the device tree usage page
 at devicetree.org\ [1]_.
 
-.. [1] http://devicetree.org/Device_Tree_Usage
+.. [1] https://elinux.org/Device_Tree_Usage
 
 The "Open Firmware Device Tree", or simply Device Tree (DT), is a data
 structure and language for describing hardware.  More specifically, it