md/raid1: simplify raid1_write_request() error handling

md/raid1: simplify raid1_write_request() error handling

raid1_write_request() increments rdev->nr_pending before checking the
badblocks and then immediately decrements it again when a device is
skipped. Move the increment until after the checks succeed so the
reference accounting is easier to follow.

Consolidate the failure paths so that each error label releases exactly
the resources acquired up to that point. err_dec_pending drops pending
references and frees the r1bio, while err_allow_barrier handles the
barrier release before returning.

When a REQ_ATOMIC write cannot be satisfied due to a badblock range,
complete the bio with BLK_STS_NOTSUPP rather than reporting an I/O
error, since the operation is unsupported rather than having failed
during I/O.

Rename max_write_sectors to max_sectors and remove the redundant local
copy.

Signed-off-by: Abd-Alrhman Masalkhi <abd.masalkhi@gmail.com>
Link: https://patch.msgid.link/20260613182810.1317258-5-abd.masalkhi@gmail.com
Signed-off-by: Yu Kuai <yukuai@fygo.io>