can: mcp251xfd: fix detection of mcp251863

can: mcp251xfd: fix detection of mcp251863

In commit e583c00d7447 ("can: mcp251xfd: add support for mcp251863")
support for the mcp251863 was added. However it was not taken into
account that the auto detection of the chip model cannot distinguish
between mcp2518fd and mcp251863 and would lead to a warning message if
the firmware specifies a mcp251863.

Fix auto detection: If a mcp2518fd compatible chip is found, keep the
mcp251863 if specified by firmware, use mcp2518fd instead.

Link: https://lore.kernel.org/all/20220706064835.1848864-1-mkl@pengutronix.de
Fixes: e583c00d7447 ("can: mcp251xfd: add support for mcp251863")
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>