ring-buffer: Fix typos in function ring_buffer_producer

Fix spelling and other typos

Link: http://lkml.kernel.org/r/1573916755-32478-1-git-send-email-xianting_tian@126.com



Signed-off-by: Xianting Tian <xianting_tian@126.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>