ARM: at91/dt: fix usb0 clocks definition in sam9n12 dtsi

udphs_clk (USB Device Controller clock) is referenced instead of
uhphs_clk (USB Host Controller clock).

Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>