net: marvell: Use min() instead of doing it manually

Fix following coccicheck warning:
drivers/net/ethernet/marvell/mv643xx_eth.c:1664:35-36: WARNING opportunity for min()

Signed-off-by: Haowen Bai <baihaowen88@gmail.com>
Link: https://lore.kernel.org/r/1646271529-7659-1-git-send-email-baihaowen88@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>