can: mcp251xfd: mcp251xfd_ring_init(): check TX-coalescing configuration

can: mcp251xfd: mcp251xfd_ring_init(): check TX-coalescing configuration

When changing the interface from CAN-CC to CAN-FD mode the old
coalescing parameters are re-used. This might cause problem, as the
configured parameters are too big for CAN-FD mode.

During testing an invalid TX coalescing configuration has been seen.
The problem should be been fixed in the previous patch, but add a
safeguard here to ensure that the number of TEF coalescing buffers (if
configured) is exactly the half of all TEF buffers.

Link: https://lore.kernel.org/all/20240805-mcp251xfd-fix-ringconfig-v1-2-72086f0ca5ee@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>