memory: Update description of memory_region_is_mapped()

Let's update the documentation, making it clearer what the semantics
of memory_region_is_mapped() actually are.

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20211102164317.45658-4-david@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
diff --git a/include/exec/memory.h b/include/exec/memory.h
index fea1a49..63be794 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -2297,7 +2297,8 @@
 
 /**
  * memory_region_is_mapped: returns true if #MemoryRegion is mapped
- * into any address space.
+ * into another memory region, which does not necessarily imply that it is
+ * mapped into an address space.
  *
  * @mr: a #MemoryRegion which should be checked if it's mapped
  */