tracing: Remove local variable for argument detection from trace_printk()

tracing: Remove local variable for argument detection from trace_printk()

The trace_printk() macro uses a local variable _______STR to detect
whether variadic arguments are present. This name can shadow outer
variables.

Replace the local variable with sizeof applied directly to the
stringified arguments:

  if (sizeof __stringify((__VA_ARGS__)) > 3)

This eliminates the shadowing risk entirely without introducing
any additional includes or local variables.

Verified with objdump on samples/trace_printk that all four cases
branch correctly: __trace_bputs, __trace_puts, __trace_bprintk,
and __trace_printk.

Link: https://patch.msgid.link/20260502075535.34997-1-tiffany019230@gmail.com
Suggested-by: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Qian-Yu Lin <tiffany019230@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>