usb: gadget: f_ncm: allow using NCM in SuperSpeed Plus gadgets.

[ Upstream commit 7974ecd7d3c0f42a98566f281e44ea8573a2ad88 ]

Currently, enabling f_ncm at SuperSpeed Plus speeds results in an
oops in config_ep_by_speed because ncm_set_alt passes in NULL
ssp_descriptors. Fix this by re-using the SuperSpeed descriptors.
This is safe because usb_assign_descriptors calls
usb_copy_descriptors.

Tested: enabled f_ncm on a dwc3 gadget and 10Gbps link, ran iperf
Reviewed-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: Lorenzo Colitti <lorenzo@google.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>