rocker: Add missing break for PRE_BRIDGE_FLAGS

A missing break keyword should have been added after adding support for
PRE_BRIDGE_FLAGS.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 93700458

 ("rocker: Check Handle PORT_PRE_BRIDGE_FLAGS")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>