dt-bindings: usb: ci-hdrc-usb2: Fix clocks/clock-names maxItems

imx35.dtsi has three USB clocks. Adjust the maxItems to fix the following
schema warnings:

imx35-eukrea-mbimxsd35-baseboard.dtb: usb@53ff4400: clock-names: ['ipg', 'ahb', 'per'] is too long

Signed-off-by: Fabio Estevam <festevam@denx.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230731144422.1532498-2-festevam@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>