tracing: Add printf attribute to log function

Attributing the function allows the compiler to more thoroughly
check the use of the function with -Wformat and similar flags.

Link: https://lkml.kernel.org/r/20201221162715.3757291-1-trix@redhat.comSigned-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

include/linux/trace.h

@@ -34,6 +34,7 @@ int unregister_ftrace_export(struct trace_export *export);
 struct trace_array;
 
 void trace_printk_init_buffers(void);
+__printf(3, 4)
 int trace_array_printk(struct trace_array *tr, unsigned long ip,
 		       const char *fmt, ...);
 int trace_array_init_printk(struct trace_array *tr);