clk: at91: usb: fix determine_rate prototype again

We had an incorrect backport of
45912431 ("clk: at91: usb: propagate rate modification to the parent clk")
that was fixed incorrectly in linux-3.18.y by
76723e7e ("clk: at91: usb: fix determine_rate prototype")

as shown by this warning:

drivers/clk/at91/clk-usb.c:155:20: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]
drivers/clk/at91/clk-usb.c:193:20: warning: initialization from incompatible pointer type [-Wincompatible-pointer-types]

This should fix it properly.

Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>