Fix VPRetinaCluster edge-flag encoding

This MR introduces a bug-fix in the encoding of the edge flag of the RetinaClusters.

Impact:

• The edge bit is not currently used in any decoding at HLT; it is not used for tracking nor any offline reconstruction. Consequently, there is no impact associated with this change.

Details:

1. RetinaCluster are reconstructed out of non-isolated SuperPixels by grouping the neighbouring SPs into a SP matrix ( VPRetinaMatrix.cpp).
2. All pixels in the matrix are checked to verify if they can represent the anchor (bottom-left) of a (3pixels x 3pixels) sub-matrix where the RetinaCluster will be reconstructed.
3. All pixels whose 3x3 submatrix touches or crosses the boundaries of the SP matrix are flagged as edge.
4. The ideal flagging is the following (the pixels flagged as edge are the orange ones):

5. The flag encoding of the current code is:

6. This MR fixes one of the checking columns of the edge flagging, in order to make it consistent with the figure in bullet 4.

FYI: @flazzari