Fixed size of m_aiGpmIntraMPMLists

Fixes issue #98 (closed) on the size of m_aiGpmIntraMPMLists introduced by AJ0107. AJ0107 wrongly increased the size from [64][2][3] to [112][2][3]. The size increase has been reverted and the correct indices are used to access this array. A small test (1 intra period, MTT depth set to 1 on class D) confirms that there is no BD-rate change and that the updated software can decode the un-updated one.