swift: Increase read-write volume to 32MB

Swift will be using UBI for its filesystem. Since it has 128MB flash
chips, increase the size of the read-write volume to 32MB, same as
witherspoon-128.

Change-Id: If5a6930ddeb2326a2ffdb19f1466b863eaa93fda
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
1 file changed