Fix typo in ganeti-os-interface(7)

The variable is called “IMPORT_INDEX”, not “IMPORT_IDX”.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

man/ganeti-os-interface.sgml

@@ -22,6 +22,7 @@
       <year>2007</year>
       <year>2008</year>
       <year>2009</year>
+      <year>2010</year>
       <holder>Google Inc.</holder>
     </copyright>
     &dhdate;
@@ -273,7 +274,7 @@
 
       <para>
         The difference in variables is that the current disk is called
-        by <envar>IMPORT_DEVICE</envar> and <envar>IMPORT_IDX</envar>
+        by <envar>IMPORT_DEVICE</envar> and <envar>IMPORT_INDEX</envar>
         (instead of <emphasis>EXPORT_</emphasis>).
       </para>