[SCSI] sd: Fix overflow with big physical blocks

The hw_sector_size variable could overflow if a device reported huge
physical blocks.  Switch to the more accurate physical_block_size
terminology and make sure we use an unsigned int to match the range
permitted by READ CAPACITY(16).

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>