rcuperf: Fix perf_type module-parameter description

The rcu_bh rcuperf type was removed by commit 620d2460("rcuperf:
Remove the "rcu_bh" and "sched" torture types"), but it lives on in the
MODULE_PARM_DESC() of perf_type.  This commit therefore changes that
module-parameter description to substitute srcu for rcu_bh.
Signed-off-by: Xiao Yang <ice_yangxiao@163.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

kernel/rcu/rcuperf.c

@@ -89,7 +89,7 @@ torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable
 
 static char *perf_type = "rcu";
 module_param(perf_type, charp, 0444);
-MODULE_PARM_DESC(perf_type, "Type of RCU to performance-test (rcu, rcu_bh, ...)");
+MODULE_PARM_DESC(perf_type, "Type of RCU to performance-test (rcu, srcu, ...)");
 
 static int nrealreaders;
 static int nrealwriters;