tracing/histogram: Wrap remaining shell snippets in code blocks

Most shell command snippets (echo/cat) and their output are already in
literal code blocks. However a few still isn't wrapped, in which the
htmldocs output is ugly.

Wrap the remaining unwrapped snippets, while also fix recent kernel test
robot warnings.

Link: https://lore.kernel.org/linux-trace-kernel/20230129031402.47420-1-bagasdotme@gmail.com

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/linux-doc/202301290253.LU5yIxcJ-lkp@intel.com/


Fixes: 88238513 ("tracing/histogram: Document variable stacktrace")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>