ehci-platform: add the max clock number to 4

Allwinner A64 EHCI requires 4 clocks to be enabled.

Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>