selftests: mlxsw: Fix typo in qos_mc_aware.sh

This patch fix some spelling typo in qos_mc_aware.sh

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>