Commit a5afc167 ("net: phy: mscc: add support for VSC8584 PHY")
introduced a call to 'phy_write' storing its return value to a variable
called 'ret'. But 'ret' never was checked for a possible error being
returned, and hence was not used at all. Fix this by checking the return
value and exiting the function if an error was returned.

As this does not fix a known bug, this commit is mostly cosmetic and not
sent as a fix.
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>