tools lib traceevent: Cleanup realloc use

tools lib traceevent: Cleanup realloc use

The if branch is completely unnecessary since 'realloc' can handle
NULL pointers for the first parameter.

This patch is just an adoption of Ulrich Drepper's recent patch on
perf tools.

Signed-off-by: Namhyung Kim <namhyung.kim@lge.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ulrich Drepper <drepper@gmail.com>
Link: http://lkml.kernel.org/r/1335230984-7613-1-git-send-email-namhyung.kim@lge.com
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>