[SCSI] Bogus disk geometry on large disks

We currently stuff a truncated size into the geometry logic and return the
result which can produce bizarre reports for a 4Tb array.  Since that
mapping logic isn't useful for disks that big don't try and map this way at
all.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>