ring-buffer: Fix a bunch of typos in comments

An anonymous source sent me a bunch of typo fixes in the comments of
ring_buffer.c file. That source did not want to be associated to this patch
because they don't want to be known as "one of those" commiters (you know who
you are!). They gave me permission to sign this off in my own name.

Suggested-by:  <One-of-those-commiters@YouKnowWhoYouAre.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>