scsi: sd: Be consistent about blocks vs. sectors

We have had several bugs due mixing sector and logical block size
terminology. In the block layer, a sector is a 512-byte unit regardless of
the logical block size of the underlying device. But the term "sector" is
still widely used in sd.c when referring to logical block sized units.

We previously introduced helper functions such as sectors_to_logical() and
logical_to_sectors() to make the distinction clear. Use these to make the
code in sd.c consistent wrt. logical blocks and block layer sectors.

Use "lba" to describe a logical block address and "nr_blocks" when counting
logical blocks. SBC uses "TRANSFER LENGTH" to describe the latter but this
term was avoided to prevent confusion with the very similar DMA transfer
size (->transfersize) which is counted in bytes.
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
[ bvanassche: ported this patch from kernel v4.11 to kernel v5.0 ]
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>