dt-bindings: sram: narrow regex for unit address to hex numbers

Regular expression used to match the unit address part should not allow
non-hex numbers.
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://lore.kernel.org/r/20240123083450.20996-1-krzysztof.kozlowski@linaro.orgSigned-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>

Documentation/devicetree/bindings/sram/allwinner,sun4i-a10-system-control.yaml

@@ -56,7 +56,7 @@ properties:
   ranges: true
 
 patternProperties:
-  "^sram@[a-z0-9]+":
+  "^sram@[a-f0-9]+":
     $ref: /schemas/sram/sram.yaml#
     unevaluatedProperties: false