Block: Fix whole_disk attribute bug

The "whole_disk" attribute was not properly converted in the block
device conversion earlier, and if the file is read, bad things can
happen.  This patch fixes this, making the attribute an empty one,
preserving the original functionality.

Many thanks to David Miller for finding this, and pointing me in the
proper place within the block code to look.

Acked-by: David S. Miller <davem@davemloft.net>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>