dm cache: actually resize cache

Commit f494a9c6

 ("dm cache: cache
shrinking support") broke cache resizing support.

dm_cache_resize() is called with cache->cache_size before it gets
updated to new_size, so it is a no-op.  But the dm-cache superblock is
updated with the new_size even though the backing dm-array is not
resized.  Fix this by passing the new_size to dm_cache_resize().

Signed-off-by: Vincent Pelletier <plr.vincent@gmail.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>