dm: fold dm_process_bio() into dm_submit_bio()

dm_process_bio() is only called by dm_submit_bio(), there is no benefit
to keeping dm_process_bio() factored out, so fold it.

While at it, cleanup dm_submit_bio()'s DMF_BLOCK_IO_FOR_SUSPEND related
branching and expand scope of dm_get_live_table() rcu reference on map
via common 'out' label to dm_put_live_table().

Signed-off-by: Mike Snitzer <snitzer@redhat.com>