net: remove else after return in dev_prep_valid_name()

Remove unnecessary else clauses after return.
I copied this if / else construct from somewhere,
it makes the code harder to read.

Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Link: https://lore.kernel.org/r/20231023152346.3639749-7-kuba@kernel.org


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