dt-bindings: display: samsung,exynos-mixer: Fix 'regs' typo

The correct property name is 'reg' not 'regs'.

Fixes: 68e89bb3 ("dt-bindings: display: samsung,exynos-mixer: convert to dtschema")
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

Documentation/devicetree/bindings/display/samsung/samsung,exynos-mixer.yaml

@@ -85,7 +85,7 @@ allOf:
         clocks:
           minItems: 6
           maxItems: 6
-        regs:
+        reg:
           minItems: 2
           maxItems: 2
 
@@ -99,7 +99,7 @@ allOf:
         clocks:
           minItems: 4
           maxItems: 4
-        regs:
+        reg:
           minItems: 2
           maxItems: 2
 
@@ -116,7 +116,7 @@ allOf:
         clocks:
           minItems: 3
           maxItems: 3
-        regs:
+        reg:
           minItems: 1
           maxItems: 1