[PATCH for 5.1] docs: fix trace docs build with sphinx 3.1.1

["Daniel P. Berrangé" <berrange@redhat.com>]

In Fedora 33 rawhide, we now have sphinx 3.1.1, as opposed
to previous 2.2.2. This new version generates a warning on
the source:

docs/qemu-option-trace.rst.inc:4:Malformed option description
  '[enable=]PATTERN', should look like "opt", "-opt args",
  "--opt args", "/opt args" or "+opt args"

This turns into an error when QEMU passes -W to sphinx-build

Strangely the previous 2.2.2 code has the exact same logic
for checking the syntax, but it is not being triggered. While
it is only complaining about the first option, I changed all
the options to give consistency.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 docs/qemu-option-trace.rst.inc | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/docs/qemu-option-trace.rst.inc b/docs/qemu-option-trace.rst.inc
index 7e09773a9c..e79b0b43fc 100644
--- a/docs/qemu-option-trace.rst.inc
+++ b/docs/qemu-option-trace.rst.inc
@@ -1,7 +1,7 @@
 
 Specify tracing options.
 
-.. option:: [enable=]PATTERN
+.. option:: -trace [enable=]PATTERN
 
   Immediately enable events matching *PATTERN*
   (either event name or a globbing pattern).  This option is only
@@ -11,7 +11,7 @@ Specify tracing options.
 
   Use :option:`-trace help` to print a list of names of trace points.
 
-.. option:: events=FILE
+.. option:: -trace events=FILE
 
   Immediately enable events listed in *FILE*.
   The file must contain one event name (as listed in the ``trace-events-all``
@@ -19,7 +19,7 @@ Specify tracing options.
   available if QEMU has been compiled with the ``simple``, ``log`` or
   ``ftrace`` tracing backend.
 
-.. option:: file=FILE
+.. option:: -trace file=FILE
 
   Log output traces to *FILE*.
   This option is only available if QEMU has been compiled with
-- 
2.24.1