mlxsw: spectrum_dcb: Fix a spelling typo in spectrum_dcb.c

This patch fixes a spelling typo in spectrum_dcb.c

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