dt-bindings: mtd: nand: Standardize the child node name

In almost all the schema mentioning a NAND chip child node, the name of
the subnode contains a single index number.

In practice there are currently no controller supporting more than 8 cs
so even the [a-f] numbers are not needed. But let's be safe and limit
the number of touched files by just allow a single number everywhere, so
in practice up to 16 CS at most. This value can anyway be limited in
each schema.

Signed-off-by: Miquel Raynal <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/[e-mail]

Documentation/devicetree/bindings/mtd/allwinner,sun4i-a10-nand.yaml

···
     const: rxtx
 
 patternProperties:
-  "^nand@[a-f0-9]+$":
+  "^nand@[a-f0-9]$":
     type: object
     properties:
       reg:

Documentation/devicetree/bindings/mtd/intel,lgm-ebunand.yaml

···
       - const: rx
 
 patternProperties:
-  "^nand@[a-f0-9]+$":
+  "^nand@[a-f0-9]$":
     type: object
     properties:
       reg: