Casting function pointers breaks control flow enforcement and is
generally a horrible coding style.

Add two wrappers to get rid of these casts.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Sven Peter <sven@svenpeter.dev>
Signed-off-by: Jens Axboe <axboe@kernel.dk>