net: dsa: mv88e6xxx: pass directly chip structure to mv88e6xxx_phy_is_internal

Since this function is a simple helper, we do not need to pass a full
dsa_switch structure, we can directly pass the mv88e6xxx_chip structure.
Doing so will allow to share this function with any other function
not manipulating dsa_switch structure but needing info about number of
internal phys

Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>