Remove illegal @+ use with dimen type

Remove illegal @+ use with dimen type

@+id/foo is a way to specify an ID or create one if it doesn't exist.
This is fine to do because an ID is simply a placeholder value that is
assigned a resource ID.
@+dimen/foo doesn't make sense because there is no implicit value to
create if the resource doesn't exist.

Bug: 37716235
Test: builds
Change-Id: Ic897b208fd338bc00ac47de04ea74f0993e6a052