net: phy: realtek: clear master_slave_state if link is down

rtlgen_decode_physr() which sets master_slave_state isn't called in case
the link is down and other than rtlgen_read_status(),
rtl822x_c45_read_status() doesn't implicitely clear master_slave_state.

Avoid stale master_slave_state by always setting it to
MASTER_SLAVE_STATE_UNKNOWN in rtl822x_c45_read_status() in case the link
is down.

Fixes: 081c9c02 ("net: phy: realtek: read duplex and gbit master from PHYSR register")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Reviewed-by: Michal Swiatkowski <michal.swiatkowski@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>