tracing: Fix typo from "static inlin" to "static inline"

The trace.h header when called without CONFIG_EVENT_TRACING enabled
(seldom done), will not compile because of a typo in the protocol
of trace_event_enum_update().

Cc: stable@vger.kernel.org # 4.1+
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>