Documentation: Fix misconversion of #if

At some stage of the conversion pipeline, something thought that the
DocBook entity # should be rendered as NUM instead of #.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/Documentation/kernel-hacking/hacking.rst b/Documentation/kernel-hacking/hacking.rst
index 5192d7f..9999c84 100644
--- a/Documentation/kernel-hacking/hacking.rst
+++ b/Documentation/kernel-hacking/hacking.rst
@@ -690,8 +690,8 @@
 not tested for it. It is still possible, but not recommended. If you
 really want to do this, forget about exceptions at least.
 
-NUMif
------
+#if
+---
 
 It is generally considered cleaner to use macros in header files (or at
 the top of .c files) to abstract away functions rather than using \`#if'