can: mcp251xfd: mcp251xfd.h: sort function prototypes

The .c files in the Makefile are ordered alphabetically. This patch
groups the function prototypes by their corresponding .c file and
brings the into the same order.

Link: https://lore.kernel.org/all/20220105154300.1258636-8-mkl@pengutronix.de


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>