USB: gadget: fix rndis working at high speed

Fix a bug specific to highspeed mode in the recently updated RNDIS
support:  it wasn't setting up the high speed notification endpoint,
which prevented high speed RNDIS links from working.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Tested-by: Anand Gadiyar <gadiyar@ti.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>