[PATCH] docs: fix broken reference

[John Snow <jsnow@redhat.com>]

Long story short, we need a space here for the reference to work
correctly.


Longer story:

Without the space, kerneldoc generates a line like this:

one of :c:type:`MemoryListener.region_add\(\) <MemoryListener>`,:c:type:`MemoryListener.region_del\(\)

Sphinx does not process the role information correctly, so we get this
(my pseudo-notation) construct:

<text>,:c:type:</text>
<reference target="MemoryListener">MemoryListener.region_del()</reference>

which does not reference the desired entity, and leaves some extra junk
in the rendered output. See
https://qemu-project.gitlab.io/qemu/devel/memory.html#c.MemoryListener
member log_start for an example of the broken output as it looks today.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 include/exec/memory.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index 5728a681b27..3b9ca696061 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -571,7 +571,7 @@ struct MemoryListener {
      * @log_start:
      *
      * Called during an address space update transaction, after
-     * one of #MemoryListener.region_add(),#MemoryListener.region_del() or
+     * one of #MemoryListener.region_add(), #MemoryListener.region_del() or
      * #MemoryListener.region_nop(), if dirty memory logging clients have
      * become active since the last transaction.
      *
-- 
2.30.2