TTY: simserial, final cleanup

* remove pointless checks (tty cannot be NULL at that points)
* fix some printks (use __func__, print text directly w/o using global
  strings)
* remove some empty lines

This is the last patch for simserial. Overall, the driver is 400 lines
shorter. Being now at 560 lines.

It was tested using ski with a busybox userspace.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>