staging: dpaa2-ethsw: fix switch/case fallthrough warning

Fix the fallthrough warning that is reported by checkpatch.

Signed-off-by: Marian Posteuca <posteuca@mutex.one>
Link: https://lore.kernel.org/r/20200720064205.10323-1-posteuca@mutex.one


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>