tracing: Remove NULL check from current in tracing_generic_entry_update().

I can't imagine when or why `current' would return a NULL pointer. This
check was added in commit
      72829bc3 ("ftrace: move enums to ftrace.h and make helper function global")

but it doesn't give me hint why it was needed.

Assume `current' never returns a NULL pointer and remove the check.

Link: https://lkml.kernel.org/r/20210125194511.3924915-5-bigeasy@linutronix.de



Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>