net: dsa: realtek-smi: fix indirect reg access for ports>3

This switch family can have up to 8 UTP ports {0..7}. However,
INDIRECT_ACCESS_ADDRESS_PHYNUM_MASK was using 2 bits instead of 3,
dropping the most significant bit during indirect register reads and
writes. Reading or writing ports 4, 5, 6, and 7 registers was actually
manipulating, respectively, ports 0, 1, 2, and 3 registers.

This is not sufficient but necessary to support any variant with more
than 4 UTP ports, like RTL8367S.

rtl8365mb_phy_{read,write} will now returns -EINVAL if phy is greater
than 7.

Fixes: 4af2950c

 ("net: dsa: realtek-smi: add rtl8365mb subdriver for RTL8365MB-VC")
Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>