can: ucan: refactor endpoint lookup

Use the common USB helpers for looking up bulk and interrupt endpoints
(and determining endpoint numbers and max packet sizes) instead of open
coding.

Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://patch.msgid.link/20260330101817.1664787-3-johan@kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>