DocBook/drm: Insert `()' after function name

Signed-off-by: NMichael Witten <mfwitten@gmail.com>

Documentation/DocBook/drm.tmpl

@@ -433,15 +433,15 @@
 	</para>
 	<para>
 	  Once your global TTM accounting structure is set up and initialized
-	  by calling ttm_global_item_ref on it,
+	  by calling ttm_global_item_ref() on it,
 	  you need to create a buffer object TTM to
 	  provide a pool for buffer object allocation by clients and the
 	  kernel itself.  The type of this object should be TTM_GLOBAL_TTM_BO,
 	  and its size should be sizeof(struct ttm_bo_global).  Again,
 	  driver specific init and release functions may be provided,
-	  likely eventually calling ttm_bo_global_init and
-	  ttm_bo_global_release, respectively.  Also, like the previous
-	  object, ttm_global_item_ref is used to create an initial reference
+	  likely eventually calling ttm_bo_global_init() and
+	  ttm_bo_global_release(), respectively.  Also, like the previous
+	  object, ttm_global_item_ref() is used to create an initial reference
 	  count for the TTM, which will call your initialization function.
 	</para>
       </sect3>