net: stmmac: add aux timestamps fifo clearance wait

net: stmmac: add aux timestamps fifo clearance wait

Add timeout polling wait for auxiliary timestamps snapshot FIFO clear bit
(ATSFC) to clear. This is to ensure no residue fifo value is being read
erroneously.

Fixes: f4da56529da6 ("net: stmmac: Add support for external trigger timestamping")
Cc: <stable@vger.kernel.org> # 5.10.x
Signed-off-by: Noor Azura Ahmad Tarmizi <noor.azura.ahmad.tarmizi@intel.com>
Link: https://lore.kernel.org/r/20230111050200.2130-1-noor.azura.ahmad.tarmizi@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>