dt-bindings: pwm: mediatek: Remove gratuitous compatible string for MT7629

The MT7629 is, in fact, not compatible with the MT7622 because the
former has a single PWM channel while the former has 6. Remove the
gratuitous compatible string for MT7629.
Reported-by: Sam Shih <sam.shih@mediatek.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

Documentation/devicetree/bindings/pwm/pwm-mediatek.txt

@@ -6,7 +6,7 @@ Required properties:
    - "mediatek,mt7622-pwm": found on mt7622 SoC.
    - "mediatek,mt7623-pwm": found on mt7623 SoC.
    - "mediatek,mt7628-pwm": found on mt7628 SoC.
-   - "mediatek,mt7629-pwm", "mediatek,mt7622-pwm": found on mt7629 SoC.
+   - "mediatek,mt7629-pwm": found on mt7629 SoC.
    - "mediatek,mt8516-pwm": found on mt8516 SoC.
  - reg: physical base address and length of the controller's registers.
  - #pwm-cells: must be 2. See pwm.txt in this directory for a description of