drbd: use get_random_u64() where appropriate

drbd: use get_random_u64() where appropriate

Use the typed random integer helpers instead of
get_random_bytes() when filling a single integer variable.
The helpers return the value directly, require no pointer
or size argument, and better express intent.

Signed-off-by: David Carlier <devnexen@gmail.com>
Reviewed-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Link: https://patch.msgid.link/20260405154704.4610-1-devnexen@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>