When the PHY's strap register is read to determine if lane swapping is
needed the phy_read_mmd returns the value back into the ret variable.

If the call to read the strap fails the failed value is returned.  If
the call to read the strap is successful then ret is possibly set to a
non-zero positive number. Without reseting the ret value to 0 this will
cause the parse DT function to return a failure.

Fixes: c4566aec ("net: phy: dp83869: Update port-mirroring to read straps")
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>