scftorture: Make torture_type static

Fix the 'make C=1' warning:
kernel/scftorture.c:71:6: warning: symbol 'torture_type' was not declared. Should it be static?

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>