btrfs: adjust while loop condition in run_delalloc_nocow

We have the following pattern

while (1) {
	if (cur_offset > end)
		break;
}

Which is just

while (cur_offset <= end) {
	...
}

so adjust the code to be more clear.

Reviewed-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>