net: phy: broadcom: Use strlcpy() for ethtool::get_strings

commit 8a17eefa235f73b60c0ca7d397d2e4f66f85f413 upstream.

Our statistics strings are allocated at initialization without being
bound to a specific size, yet, we would copy ETH_GSTRING_LEN bytes using
memcpy() which would create out of bounds accesses, this was flagged by
KASAN. Replace this with strlcpy() to make sure we are bound the source
buffer size and we also always NUL-terminate strings.

Fixes: 820ee17b ("net: phy: broadcom: Add support code for reading PHY counters")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>