ata: libata-scsi: Use correct device no in ata_find_dev()

For devices not attached to a port multiplier and managed directly by
libata, the device number passed to ata_find_dev() must always be lower
than the maximum number of devices returned by ata_link_max_devices().
That is 1 for SATA devices or 2 for an IDE link with master+slave
devices. This device number is the SCSI device ID which matches these
constraints as the IDs are generated per port and so never exceed the
maximum number of devices for the link being used.

However, for libsas managed devices, SCSI device IDs are assigned per
struct scsi_host, leading to device IDs for SATA devices that can be
well in excess of libata per-link maximum number of devices. This
results in ata_find_dev() to always return NULL for libsas managed
devices except for the first device of the target scsi_host with ID
(device number) equal to 0. This issue is visible by executing the
hdparm utility, which fails. E.g.:

hdparm -i /dev/sdX
/dev/sdX:
  HDIO_GET_IDENTITY...