usb: core: Change usb_create_sysfs_intf_files()' return type to void

The usb_create_sysfs_intf_files() function always returned zero even
if it failed to create sysfs fails.  Since this is a desired behaviour
there is no need to return return code at all.  This commit changes
function's return type (form int) to void.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>