USB: Remove unneeded void * casts in core files

The patch removes unneeded casts for the following (void *) pointers:
 - struct file: private
 - struct urb: context
 - struct usb_bus: hcpriv
 - return value of kmalloc()

The patch also contains some whitespace cleanup in the relevant areas.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>