tracing: fprobe-event: Allocate string buffers from heap

Allocate temporary string buffers for fprobe-event from heap
instead of stack. This fixes the stack frame exceed limit error.

Link: https://lore.kernel.org/all/175323426643.57270.6657152008331160704.stgit@devnote2/



Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202506240416.nZIhDXoO-lkp@intel.com/


Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>