osdep/linux/hostdisk: Modify sector by sysfs as disk sector

osdep/linux/hostdisk: Modify sector by sysfs as disk sector

The disk sector size provided by sysfs file system considers the sector
size of 512 irrespective of disk sector size, thus causing the read by
the GRUB to an incorrect offset from what was originally intended.

Considering the 512 sector size of sysfs data the actual sector needs to
be modified corresponding to disk sector size.

Signed-off-by: Mukesh Kumar Chaurasiya <mchauras@linux.vnet.ibm.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>