net: dsa: lan9303: phy_addr_sel_strap rename and retype

chip->phy_addr_sel_strap is declared as a bool, but is also used as an
integer address base.

Rename 'phy_addr_sel_strap' to 'phy_addr_base', and change type to int.

Signed-off-by: Egil Hjelmeland <privat@egil-hjelmeland.no>
Signed-off-by: David S. Miller <davem@davemloft.net>