dpaa: fix 32-bit build

Book-E powerpc uses 64-bit vm_paddr_t, and 32-bit powerpc has 32-bit pointers,
so gcc errors with cast to pointer from integer of different size. As this will
not actually be used in reality anyway, simply quiet the warning by casting
through uintptr_t.

MFC after: 3 weeks
MFC with: r343168