Suspicious RCU usage messages are reported as warnings.

Fixes: a5dd63ef ("lockdep: Use "WARNING" tag on lockdep splats")
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: NPaul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>