spi: Update clock-names property for arm pl022

PL022 has two input clocks named sspclk and apb_pclk. Current schema
refers to two notations of sspclk which are indeed same and thus one can
be dropped. Update clock-names property to reflect the same.
Signed-off-by: Kuldeep Singh <singh.kuldeep87k@gmail.com>
Link: https://lore.kernel.org/r/20220309171847.5345-1-singh.kuldeep87k@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-pl022.yaml

@@ -38,9 +38,7 @@ properties:
 
   clock-names:
     items:
-      - enum:
-          - SSPCLK
-          - sspclk
+      - const: sspclk
       - const: apb_pclk
 
   pl022,autosuspend-delay: