btrfs: integrity-checker: use kmap_local_page in __btrfsic_submit_bio

Again there is an array of pointers which must be unmapped in the correct
order.

Convert the kmap()'s to kmap_local_page() and adjust the unmapping
to work backwards through the unmapping loop.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>