drm addmap broken on 32bit archs

[Stephane M. <mar...@ic...>]

Hello,

The drm addmap code got broken with the recent switch to the hash table
implementation. Specifically, when two maps have the same adress on 32
bits, they end up with the same key and nothing is done to resolve the
collision, which results in a failind addmap. This is annoying.

Stephane