net: mvpp2: Use strscpy to handle stat strings

Use a safe strscpy call to copy the ethtool stat strings into the
relevant buffers, instead of a memcpy that will be accessing
out-of-bound data.

Fixes: 118d6298 ("net: mvpp2: add ethtool GOP statistics")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>