userguide: update path to code-update

This was moved in c4c7f4055387 ("Moved host code update to own doc") but
no one updated the makefile.

Change-Id: I2b0b3aad6d2436c9cb207a4faeff7468e54a5b2a
Signed-off-by: Joel Stanley <joel@jms.id.au>
diff --git a/Makefile b/Makefile
index e4c0f52..e12cdc8 100644
--- a/Makefile
+++ b/Makefile
@@ -14,7 +14,7 @@
 	$(tex) $(tflags) $^
 	$(tex) $(tflags) $^
 
-userguide/userguide.tex: rest-api.tex host-management.tex console.tex code-update.tex
+userguide/userguide.tex: rest-api.tex host-management.tex console.tex code-update/code-update.tex
 
 %.tex: %.md
 	pandoc -o $@ $^