can: mcp251xfd: mcp25xxfd_ring_alloc(): add define instead open coding the...

can: mcp251xfd: mcp25xxfd_ring_alloc(): add define instead open coding the maximum number of RX objects

This patch add a define for the maximum number of RX objects instead of open
coding it.

Link: https://lore.kernel.org/r/20201126132144.351154-2-mkl@pengutronix.de


Tested-by: Thomas Kopp <thomas.kopp@microchip.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>