brd: use cond_resched instead of cond_resched_rcu

brd: use cond_resched instead of cond_resched_rcu

The body of the loop is run without RCU lock held. Use the regular
cond_resched() instead of cond_resched_rcu().

Fixes: 786bb0245881 ("brd: use XArray instead of radix-tree to index backing pages")
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20230614133538.1279369-1-p.raghav@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>