drbd: Rename kvfree_rcu() to kvfree_rcu_mightsleep()

The kvfree_rcu() macro's single-argument form is deprecated.  Therefore
switch to the new kvfree_rcu_mightsleep() variant. The goal is to
avoid accidental use of the single-argument forms, which can introduce
functionality bugs in atomic contexts and latency bugs in non-atomic
contexts.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Philipp Reisner <philipp.reisner@linbit.com>
Cc: Lars Ellenberg <lars.ellenberg@linbit.com>
Begrudgingly-acked-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>