powerpc/usb: fix type cast for address of ioremap to compatible with 64-bit

Below are codes for accessing usb sysif_regs in driver:

usb_sys_regs = (struct usb_sys_interface *)
	((u32)dr_regs + USB_DR_SYS_OFFSET);

these codes work in 32-bit, but in 64-bit, use u32 to type cast the address
of ioremap is not right, and accessing members of 'usb_sys_regs' will cause
call trace, so use (void *) for both 32-bit and 64-bit.

Signed-off-by: Shaohui Xie <Shaohui.Xie@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>