net: reduce indentation level in sk_clone_lock()

Rework initial test to jump over init code
if memory allocation has failed.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20210127152731.748663-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>