fdisk: (and cfdisk) fix to be consistent about maximum heads

fdisk: (and cfdisk) fix to be consistent about maximum heads

Fix fdisk and cfdisk to be consistent about maximum heads

Without this patch, fdisk allows up to 256 heads to be set via the menu, but
only up to 255 heads by command line -H. Similarly, cfdisk's -H option also
enforces heads <= 255 instead of heads <= 256.

The strange limit of 256 comes about because (heads - 1) should fit in a
single byte for legacy CHS. Geometries of 256 heads and 32 sectors are seen
in disks from other operating systems where cylinder-aligned partitions
which are also aligned to a 4MB boundary are wanted.

Signed-off-by: Chris Webb <chris@arachsys.com>