stmmac: fix for hw timestamp of GMAC3 unit

1.) Bugfix of function stmmac_get_tx_hwtstamp.
    Corrected the tx timestamp available check (same as 4.8 and older)
    Change printout from info syslevel to debug.

2.) Bugfix of function stmmac_get_rx_hwtstamp.
    Corrected the rx timestamp available check (same as 4.8 and older)
    Change printout from info syslevel to debug.

Fixes: ba1ffd74

 ("stmmac: fix PTP support for GMAC4")
Signed-off-by: Mario Molitor <mario_molitor@web.de>
Signed-off-by: David S. Miller <davem@davemloft.net>