Allocator: fix the caching of host va size

Commit abf9724 ("Allocator: Fix and optimize VA range detection")
removed assignment to the `HostVASize` global thus making each call to
`DetermineVASize` redo all the work with potential to produce incorrect
results. Set the global again to fix this.

FEXCore/Source/Utils/Allocator.cpp

@@ -125,6 +125,7 @@ FEX_DEFAULT_VISIBILITY size_t DetermineVASize() {
       ::munmap(Ptr, FEXCore::Utils::FEX_PAGE_SIZE);
     }
     if (Ptr != (void*)~0ULL || errno == EEXIST) {
+      HostVASize = Bits;
       return Bits;
     }
   }