staging: fsl-dpaa2/ethsw: Fix uninitialized variables

Functions port_vlans_add() and port_vlans_del() could,
in theory, return an uninitialized variable. Fix this
by initializing the variable in question at declaration.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>