docs: ftrace: Fix minor issues in the doc

I didn't want to be pushy with these minor fixes but occur to me now that, even all seem to be clear in the latest version of the RFC (v2) related to these fixes, a clean patchset could be expected after the RFC. So here we go:

Clarifies the RAM footprint of buffer_size_kb without getting into implementation details.

Fix typos and a small notation mistakes in the doc.

Changes in this patchset (since RFC v2)
- Take out the notation mistake into its own commit because it is not a typo.

Changes in RFC v2:
- Removes implementation description of the RAM footprint of buffer_size_kb, but still make the corresponded clarification.

- Removes a patch that was just for illustration purposes because Steven already got the issue that I was referring to.

- Adds a patch to fix other typos in the doc.

Frank A. Cancio Bello (3):
docs: ftrace: Clarify the RAM impact of buffer_size_kb
docs: ftrace: Fix typos
docs: ftrace: Fix small notation mistake

 Documentation/trace/ftrace.rst             | 9 +++++----
 Documentation/trace/ring-buffer-design.txt | 2 +-
 2 files changed, 6 insertions(+), 5 deletions(-)

2.17.1