ata: libata-scsi: Simplify scsi_XX_lba_len()

In scsi_10_lba_len() and scsi_16_lba_len() functions, use
get_unaligned_bexx() to access a cdb LBA and length fields instead of
hardcoding the byte retrieval. With these simplification, the functions
can also be declared inline.

Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>