Fix component size checks in validate_super0.

Fix component size checks in validate_super0.

A 0.90 array can use at most 4TB of each device - 2TB between
2.6.39 and 3.1 due to a kernel bug.

The test for this in validate_super0 is very wrong.  'size' is sectors
and the number it is compared against is just confusing.

So fix it all up and correct the spelling of terabytes and remove
a second redundant test on 'size'.

Signed-off-by: NeilBrown <neilb@suse.de>