usb: renesas_usbhs: fix platform init error message

There is a typo ("prove" instead of "probe") in the error message printed when
the platform initialization fails. Replace that word with more fitting "init".

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>