kmsan: export kmsan_handle_urb

USB support can be in a loadable module, and this causes a link failure
with KMSAN:

ERROR: modpost: "kmsan_handle_urb" [drivers/usb/core/usbcore.ko] undefined!

Export the symbol so it can be used by this module.

Link: https://lkml.kernel.org/r/20221215162710.3802378-1-arnd@kernel.org
Fixes: 553a8018

 ("kmsan: handle memory sent to/from USB")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>