net: stmmac: Remove if condition by taking advantage of hwif return code

net: stmmac: Remove if condition by taking advantage of hwif return code

We can remove the if condition and check if return code is different
than -EINVAL, meaning callback is present.

Signed-off-by: Jose Abreu <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Joao Pinto <[email protected]>
Cc: Vitor Soares <[email protected]>
Cc: Giuseppe Cavallaro <[email protected]>
Cc: Alexandre Torgue <[email protected]>
Signed-off-by: David S. Miller <[email protected]>