tools lib traceevent: Changed return logic of trace_seq_printf() and trace_seq_vprint...

tools lib traceevent: Changed return logic of trace_seq_printf() and trace_seq_vprintf() APIs

In order to make libtraceevent into a proper library, its API should be
straightforward.

The trace_seq_printf() and trace_seq_vprintf() APIs have inconsistent
returned values with the other trace_seq_* APIs.

This path changes the return logic of trace_seq_printf() and
trace_seq_vprintf() to return the number of printed characters, as the
other trace_seq_* related APIs.

Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20181201040852.485792891@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>