tracing: Add static to local functions

This patch adds static to the following functions:
-cycle_t buffer_ftrace_now
-void free_snapshot
-int trace_selftest_startup_dynamic_tracing

Link: http://lkml.kernel.org/p/20140417214442.d7abc7c0b0e4b90e7fedecc9@skynet.be



Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>