This patch converts the struct mcp251xfd_tef_ring member within the struct
mcp251xfd_priv into an array of length one. This way all rings (tef, tx and rx)
can be accessed in the same way.

Link: https://lore.kernel.org/r/20201126132144.351154-4-mkl@pengutronix.deTested-by: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>