COMP: Array versus singleton access

Coverity reports:
CID 1103095:  Out-of-bounds access  (ARRAY_VS_SINGLETON)
Taking address with "&dim" yields a singleton pointer.

Replaced singletons with arrays of proper dimension.

Change-Id: Ic2e64d0442be12ddb6e5f95523932724f3becbf0
Merge topic 'Coverity_itkHDF5ImageIO'

a977172e COMP: Array versus singleton access