dsa: mv88x6xxx: Zero statistics counters

Zero the statistics counters when setting up the global
registers. Otherwise the counters will remain from the last boot if
the power has not been removed.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx.c

@@ -2005,6 +2005,12 @@ int mv88e6xxx_setup_global(struct dsa_switch *ds)
 				  0x9000 | (i << 8));
 	}
 
+	/* Clear the statistics counters for all ports */
+	REG_WRITE(REG_GLOBAL, GLOBAL_STATS_OP, GLOBAL_STATS_OP_FLUSH_ALL);
+
+	/* Wait for the flush to complete. */
+	_mv88e6xxx_stats_wait(ds);
+
 	return 0;
 }