tracing: Make tracepoint_printk static as not exported

tracing: Make tracepoint_printk static as not exported

The tracepoint_printk symbol is not exported, so make it
static to remove the following sparse warning:

kernel/trace/trace.c:90:5: warning: symbol 'tracepoint_printk' was not declared. Should it be static?

Fixes: dd293df6395a2 ("tracing: Move trace sysctls into trace.c")
Link: https://patch.msgid.link/20260617105822.904164-1-ben.dooks@codethink.co.uk
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>