net: dsa: mv88e6xxx: fix internal PHYs for 6320 family

Fix internal PHYs definition for the 6320 family, which has only 2
internal PHYs (on ports 3 and 4).

Fixes: bc393155 ("net: dsa: mv88e6xxx: Add number of internal PHYs")
Signed-off-by: Marek Behún <kabel@kernel.org>
Cc: <stable@vger.kernel.org> # 6.6.x
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20250317173250.28780-7-kabel@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>