af_packet: remove a stray tab in packet_set_ring()

At first glance it looks like there is a missing curly brace but
actually the code works the same either way.  I have adjusted the
indenting but left the code the same.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>