net/mvpp2: fix port speed overflow
net/mvpp2: fix port speed overflow

ethtool_cmd_speed return uint32 and after the arithmetic
operation in mrvl_get_max_rate func the result is out of range.

Fixes: 429c394417 ("net/mvpp2: support traffic manager")
Cc: stable@dpdk.org

Signed-off-by: Dana Vardi <9c1c2a764bd12654d3299766a6230861354dd126@marvell.com>
Reviewed-by: Liron Himi <df7a1fcdffe73785b04dbbbb050c783d856d9736@marvell.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk