seemp: fix minor issues

- Fix ioctl handling control flow so that a request is only invalid
  if the command is unknown.
- Append a newline character to the end of an error log message.

Change-Id: Iab49c94ac5103bffc840d94da42cb0ce36a93728
Signed-off-by: Yida Wang <yidaw@codeaurora.org>