Documentation: Fix typo of reference file name

Fix a typo of Documentation/trace/fprobe.rst.

Link: https://lore.kernel.org/all/168584575125.2056209.5771945721143181243.stgit@mhiramat.roam.corp.google.com/



Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202306040144.aD72UzkF-lkp@intel.com/


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