net: dsa: b53: stop reading ARL entries if search is done

net: dsa: b53: stop reading ARL entries if search is done

The switch clears the ARL_SRCH_STDN bit when the search is done, i.e. it
finished traversing the ARL table.

This means that there will be no valid result, so we should not attempt
to read and process any further entries.

We only ever check the validity of the entries for 4 ARL bin chips, and
only after having passed the first entry to the b53_fdb_copy().

This means that we always pass an invalid entry at the end to the
b53_fdb_copy(). b53_fdb_copy() does check the validity though before
passing on the entry, so it never gets passed on.

On < 4 ARL bin chips, we will even continue reading invalid entries
until we reach the result limit.

Fixes: 1da6df85c6fb ("net: dsa: b53: Implement ARL add/del/dump operations")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20251102100758.28352-3-jonas.gorski@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>