rng: Extend the range of driveUnit

Since the max unit of virtio scsi disk is 16383, update the range of
driveUnit to it.
Signed-off-by: NHan Han <hhan@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>

docs/schemas/domaincommon.rng

@@ -6460,7 +6460,7 @@
   </define>
   <define name="driveUnit">
     <data type="string">
-      <param name="pattern">[0-9]{1,2}</param>
+      <param name="pattern">[0-9]{1,5}</param>
     </data>
   </define>
   <define name="driveSCSIUnit">