The double loop is just checking if the page for the vertical stripe
is allocated.

We can easily convert it to single loop and get rid of @stripe variable.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>