md/raid1: round up to bdev_logical_block_size in narrow_write_error

This modifies raid1's narrow_write_error to round up block_sectors to the
device's logical block size.

This prevents sd complaining about "Bad block number requested" for non-512-byte
sector disks.

Signed-off-by: Nate Dailey <nate.dailey@stratus.com>
Signed-off-by: NeilBrown <neilb@suse.de>