chapter2: fix reference to chapter6

Appendix 6 is now chapter 6.

Closes #73

Signed-off-by: Raphael Gallais-Pou <rgallaispou@gmail.com>
Link: https://lore.kernel.org/r/20250401114736.56670-1-rgallaispou@gmail.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

Author: rgallaispou

source/chapter2-devicetree-basics.rst

@@ -575,10 +575,10 @@ Example:
    if a ``phandle`` property is not present. The meaning and use of the two
    properties is identical.
 
-.. note:: Most devicetrees in :abbr:`DTS (Device Tree Syntax)` (see Appendix A) will not
-   contain explicit phandle properties. The DTC tool automatically inserts
-   the ``phandle`` properties when the DTS is compiled into the binary DTB
-   format.
+.. note:: Most devicetrees in :abbr:`DTS (Device Tree Syntax)` (see
+   :numref:`Chapter %s <chapter-devicetree-source-format>`) will not contain
+   explicit phandle properties. The DTC tool automatically inserts the
+   ``phandle`` properties when the DTS is compiled into the binary DTB format.
 
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