drm: malidp: Add the size of the superblocks when calculating total

size for AFBC buffers

The size of the superblocks being added to the total AFBC buffer size
got lost in the upstreaming process. Add it back.

Reviewed-by: Ayan Kumar Halder <ayan.halder@arm.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>