can: mcp251xfd: mcp251xfd_ring_init(): use %d to print free RAM

In case of an erroneous ring configuration more RAM than available
might be used. Change the printf modifier to a signed int to properly
print this erroneous value.

Fixes: 83daa863 ("can: mcp251xfd: ring: update FIFO setup debug info")
Link: https://lore.kernel.org/20220313083640.501791-2-mkl@pengutronix.de


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