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 <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/dsa/mv88e6xxx.c

···
 				  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;
 }