Fix this warning:
checking consistency... [...]Documentation/devicetree/bindings/mtd/m25p80.rst:: WARNING: document isn't included in any toctree
by including the document.
Signed-off-by: Robert Schwebel <r.schwebel@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>