[IPV4]: Cleanup the devinet_sysctl_register

I moved the call to kmalloc() from the *t declaration into
the code (this is confusing when a variable is initialized
with the result of some call) and removed unneeded comment
near the error path. Just like I did with the neigh ctl-s.

Besides, I fixed the goto's and the labels - they were indented
with spaces :(

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>