dm: move bio_io_error into __split_and_process_bio

Move the bio_io_error() calls directly into __split_and_process_bio().

This avoids some code duplication in later patches.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>