ring-buffer: Fix a typo in function description

s/ring_buffer_commit_discard/ring_buffer_discard_commit/

Link: https://lkml.kernel.org/r/20201112151800.14382-1-hqjagain@gmail.com



Signed-off-by: Qiujun Huang <hqjagain@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>