dt-bindings: PCI: faraday,ftpci100: Fix 'contains' schema usage

The 'contains' keyword applies to elements within an array, so
using 'items' only makes sense if the elements of the array are another
array which is not the case for 'compatible' properties.

Looking at the driver, it seems the intent was the condition should be
true when 'faraday,ftpci100' is present, so we can drop
'cortina,gemini-pci'.

Fixes: 2720b991337d ("dt-bindings: PCI: ftpci100: convert faraday,ftpci100 to YAML")
Cc: Bjorn Helgaas <[e-mail]>
Cc: Linus Walleij <[e-mail]>
Cc: [e-mail]
Signed-off-by: Rob Herring <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

Documentation/devicetree/bindings/pci/faraday,ftpci100.yaml

···
   properties:
     compatible:
       contains:
-        items:
-          - const: cortina,gemini-pci
-          - const: faraday,ftpci100
+        const: faraday,ftpci100
 then:
   required:
     - interrupt-controller