dt-bindings: Remove more cases of 'allOf' containing a '$ref'

Another round of 'allOf' removals that came in this cycle.

json-schema versions draft7 and earlier have a weird behavior in that
any keywords combined with a '$ref' are ignored (silently). The correct
form was to put a '$ref' under an 'allOf'. This behavior is now changed
in the 2019-09 json-schema spec and '$ref' can be mixed with other
keywords. The json-schema library doesn't yet support this, but the
tooling now does a fixup for this and either way works.

This has been a constant source of review comments, so let's change this
treewide so everyone copies the simpler syntax.

Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/regulator/maxim,max77826.yaml

@@ -21,8 +21,7 @@ properties:
 
   regulators:
     type: object
-    allOf:
-      - $ref: regulator.yaml#
+    $ref: regulator.yaml#
     description: |
       list of regulators provided by this controller, must be named
       after their hardware counterparts LDO[1-15], BUCK and BUCKBOOST
@@ -30,13 +29,11 @@ properties:
     patternProperties:
       "^LDO([1-9]|1[0-5])$":
         type: object
-        allOf:
-          - $ref: regulator.yaml#
+        $ref: regulator.yaml#
 
       "^BUCK|BUCKBOOST$":
         type: object
-        allOf:
-          - $ref: regulator.yaml#
+        $ref: regulator.yaml#
 
     additionalProperties: false