Documentation: net: dsa: sja1105: Remove text about taprio base-time limitation

Since commit 86db36a3 ("net: dsa: sja1105: Implement state machine
for TAS with PTP clock source"), this paragraph is no longer true. So
remove it.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>