net: ethernet: ti: cpsw_ale: Fix access to un-initialized memory

It is spurious to allocate a bitmap without initializing it.
So, better safe than sorry, initialize it to 0 at least to have some known
values.

While at it, switch to the devm_bitmap_ API which is less verbose.

Fixes: 4b41d343

 ("net: ethernet: ti: cpsw: allow untagged traffic on host port")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>