Initialize *countp to 0 in stub for softdep_flushworklist().

This allows ffs_fsync() to break out of a loop that might otherwise
be infinite on kernels compiled without the SOFTUPDATES option.
The observed symptom was a system hang at the first unmount attempt.

sys/ufs/ffs/ffs_softdep_stub.c

@@ -249,6 +249,7 @@ softdep_flushworklist(oldmnt, countp, p)
 	struct proc *p;
 {
 
+	*countp = 0;
 	return (0);
 }