UPSTREAM: tracing/histogram: Fix documentation inline emphasis warning

This fixes the warning:

Documentation/trace/histogram.rst:1766: WARNING: Inline emphasis
start-string without end-string

The issue was caused by an unescaped '*' character.

Link: https://lore.kernel.org/all/20211028170548.2597449-1-kaleshsingh@google.com/T/#m77da47432f5cc6521d4294ffdb9621949cc35d04
Link: https://lkml.kernel.org/r/20211028170548.2597449-1-kaleshsingh@google.com



Fixes: 2d2f6d4b ("tracing/histogram: Document expression arithmetic and constants")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
(cherry picked from commit 93d76e4a)

Bug: 146055070
Bug: 145972256
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Change-Id: Ie9d0738d8bb47ea7fd84917a79cad99fdefe767f