MemArena: Fix the launching of non-Wii games

When we cleaned up the code to calculate the shm_position and total_mem
in one step, we sometimes skipped over certain views because they were
Wii-only. When looking at the total memory, we'd look at the last field,
whether or not it was skipped. Since Wii-only fields are the last view,
this meant that the shm_position was 0, since it was skipped, causing us
to map a 0-sized field.

Fix this by explicitly returning the total size from
MemoryMap_InitializeViews.