torture: Make torture.sh refscale testing qualify verbose_batched

In torture.sh, the testing of refscale incorrectly used verbose_batched
as a kernel boot parameter, which causes this parameter to be passed
to the init process.  This commit therefore prefixes it with refscale,
so that refscale.verbose_batched is passed to the kernel.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>