net: phy: dp83869: Fix return paths to return proper values

Fix the return paths for all I/O operations to ensure
that the I/O completed successfully.  Then pass the return
to the caller for further processing

Fixes: 01db923e ("net: phy: dp83869: Add TI dp83869 phy")
Reported-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>