Fix slice card layout so show more button works correctly

Change padding top/bottom to margin, so the sliceview can use the full
288dp height (4 rows + see more button).

Side effect is that ripple doesn't fill the entire cardview. But it
never did anyway.

Change-Id: Ie57187fbe2b8caa2cf9d0dc31d7678eee07085f4
Fixes: 118398695
Test: visual