man: fix lib dir in which we look for config

Thanks to William Hubbs <w.d.hubbs@gmail.com> for spotting the bug.
diff --git a/man/modprobe.d.xml b/man/modprobe.d.xml
index dc19b23..7b0c298 100644
--- a/man/modprobe.d.xml
+++ b/man/modprobe.d.xml
@@ -40,7 +40,7 @@
   </refnamediv>
 
   <refsynopsisdiv>
-    <para><filename>/usr/lib/modprobe.d/*.conf</filename></para>
+    <para><filename>/lib/modprobe.d/*.conf</filename></para>
     <para><filename>/etc/modprobe.d/*.conf</filename></para>
     <para><filename>/run/modprobe.d/*.conf</filename></para>
   </refsynopsisdiv>