ARM: at91: at91sam9x5: add clocks for usb device

Add clocks for usb device, or else switch to CCF, the gadget
won't work.

Reported-by: Jiri Prchal <jiri.prchal@aksignal.cz>
Signed-off-by: Bo Shen <voice.shen@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Tested-by: Jiri Prchal <jiri.prchal@aksignal.cz>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>