dm zone: fix NULL pointer dereference in dm_zone_map_bio

Commit 0fbb4d93 ("dm: add dm_submit_bio_remap interface") changed
the alloc_io() function to delay the initialization of struct dm_io's
orig_bio member, leaving it NULL until after the dm_io and associated
user submitted bio is processed by __split_and_process_bio(). This
change causes a NULL pointer dereference in dm_zone_map_bio() when the
original user bio is inspected to detect the need for zone append
command emulation.

Fix this NULL pointer by updating dm_zone_map_bio() to not access
->orig_bio when the same info can be accessed from the clone of the
->orig_bio _before_ any ->map processing. Save off the bio_op() and
bio_sectors() for the clone and then use the saved orig_bio_details as
needed.

Fixes: 0fbb4d93 ("dm: add dm_submit_bio_remap interface")
Reported-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Tested-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>