trace: ftrace_dump_on_oops[] is not exported, make it static

The ftrace_dump_on_oops string is not used outside of trace.c so
make it static to avoid the export warning from sparse:

kernel/trace/trace.c:141:6: warning: symbol 'ftrace_dump_on_oops' was not declared. Should it be static?

Fixes: dd293df ("tracing: Move trace sysctls into trace.c")
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Ben Dooks <[email protected]>
Signed-off-by: Steven Rostedt (Google) <[email protected]>

Author: bjdooks-ct

kernel/trace/trace.c

@@ -138,7 +138,7 @@ cpumask_var_t __read_mostly	tracing_buffer_mask;
  * by commas.
  */
 /* Set to string format zero to disable by default */
-char ftrace_dump_on_oops[MAX_TRACER_SIZE] = "0";
+static char ftrace_dump_on_oops[MAX_TRACER_SIZE] = "0";
 
 /* When set, tracing will stop when a WARN*() is hit */
 static int __disable_trace_on_warning;