netfilter: nf_nat_helper: tidy up adjust_tcp_sequence

The variable 'other_way' gets initialized but is not read afterwards,
so remove it.  Pass the right arguments to a pr_debug call.

While being at tidy up a bit and it fix this checkpatch warning:
  WARNING: suspect code indent for conditional statements

Signed-off-by: Hannes Eder <heder@google.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>