net: microchip: sparx5: fix uninitialized variables

Smatch complains that "err" can be uninitialized on these paths.  Also
it's just nicer to "return 0;" instead of "return err;"

Fixes: 3a344f99

 ("net: microchip: sparx5: Add support for TC flower ARP dissector")
Signed-off-by: Dan Carpenter <error27@gmail.com>
Link: https://lore.kernel.org/r/Y3eg9Ml/LmLR3L3C@kili


Signed-off-by: Jakub Kicinski <kuba@kernel.org>