staging: fsl-dpaa2: ethsw: Remove getting PORT_BRIDGE_FLAGS

There is no code that tries to get the attribute
SWITCHDEV_ATTR_ID_PORT_BRIDGE_FLAGS, remove support for doing that.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>