dt-bindings: serial: brcm,bcm7271-uart: Constrain clocks

Lists should have fixed constraints, because binding must be specific in
respect to hardware, thus add missing constraints to number of clocks.

Cc: stable <[e-mail]>
Fixes: 88a499cd70d4 ("dt-bindings: Add support for the Broadcom UART driver")
Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

Documentation/devicetree/bindings/serial/brcm,bcm7271-uart.yaml

···
           - const: dma_intr2
 
   clocks:
-    minItems: 1
+    maxItems: 1
 
   clock-names:
     const: sw_baud