VDUSE: fix documentation underline warning

Fix a VDUSE documentation build warning:

Documentation/userspace-api/vduse.rst:21: WARNING: Title underline too short.

Fixes: 7bc7f61 ("Documentation: Add documentation for VDUSE")
Signed-off-by: Randy Dunlap <[email protected]>
Cc: Xie Yongji <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: [email protected]
Cc: Jonathan Corbet <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Michael S. Tsirkin <[email protected]>
Reviewed-by: Xie Yongji <[email protected]>
Acked-by: Jason Wang <[email protected]>

Author: rddunlap

Documentation/userspace-api/vduse.rst

@@ -18,7 +18,7 @@ types can be added after the security issue of corresponding device driver
 is clarified or fixed in the future.
 
 Create/Destroy VDUSE devices
-------------------------
+----------------------------
 
 VDUSE devices are created as follows: