net: phy: adin: fix a warning about msleep

found a warning by the following command:
./scripts/checkpatch.pl -f drivers/net/phy/adin.c

WARNING: msleep < 20ms can sleep for up to 20ms; see Documentation/timers/timers-howto.rst
 #628: FILE: drivers/net/phy/adin.c:628:
+	msleep(10);

Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>