tracing: Remove return values of most trace_seq_*() functions

The trace_seq_printf() and friends are used to store strings into a buffer
that can be passed around from function to function. If the trace_seq buffer
fills up, it will not print any more. The return values were somewhat
inconsistant and using trace_seq_has_overflowed() was a better way to know
if the write to the trace_seq buffer succeeded or not.

Now that all users have removed reading the return value of the printf()
type functions, they can safely return void and keep future users of them
from reading the inconsistent values as well.

Link: http://lkml.kernel.org/r/20141114011411.992510720@goodmis.org

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>