Revert "net: dsa: b53: Fix valid setting for MDB entries"

This reverts commit 1fae6eb0.

Upstream commit was a fix for an overlook of setting "ent.is_valid"
twice after 5d65b64a ("net: dsa: b53: Add support for MDB").

Since MDB support was not backported to stable kernels (it's not a bug
fix) there is nothing to fix there. Backporting this commit resulted in
"env.is_valid" not being set at all.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>