fdisk: use real sector size in verify() and warn_cylinders()

fdisk: use real sector size in verify() and warn_cylinders()

4KiB-sector disk:

	Note: sector size is 4096 (not 512)

	Disk /dev/sdb: 8 MB, 8388608 bytes
	8 heads, 32 sectors/track, 8 cylinders, total 2048 sectors
	Units = sectors of 1 * 4096 = 4096 bytes
	Disk identifier: 0x6aad54da

	   Device Boot      Start         End      Blocks   Id  System
	/dev/sdb1              32        2047        8064   83  Linux

old version (mix 512 and real sectors):

	Command (m for help): v
	14367 unallocated sectors

new version:

	Command (m for help): v
	31 unallocated 4096-byte sectors

Signed-off-by: Karel Zak <kzak@redhat.com>