dt-bindings: rng: update bindings for MT7629 SoC

This updates bindings for MT7629 RNG driver.
Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Acked-by: Sean Wang <sean.wang@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/rng/mtk-rng.txt

 Device-Tree bindings for Mediatek random number generator
-found in Mediatek SoC family
+found in MediaTek SoC family
 
 Required properties:
 - compatible	    : Should be
 			"mediatek,mt7622-rng", 	"mediatek,mt7623-rng" : for MT7622
+			"mediatek,mt7629-rng",  "mediatek,mt7623-rng" : for MT7629
 			"mediatek,mt7623-rng" : for MT7623
 - clocks	    : list of clock specifiers, corresponding to
 		      entries in clock-names property;