net: phy: dp83869: fix return of uninitialized variable ret

In the case where the call to phy_interface_is_rgmii returns zero
the variable ret is left uninitialized and this is returned at
the end of the function dp83869_configure_rgmii.  Fix this by
returning 0 instead of the uninitialized value in ret.

Addresses-Coverity: ("Uninitialized scalar variable")
Fixes: 01db923e ("net: phy: dp83869: Add TI dp83869 phy")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>