[PATCH] drm: fix i_mapping and f_mapping initialization in drm_open in error path

[Michal Hocko]

Hi,
the patch bellow fixes a nullptr dereference reported with OpenSUSE12.3.
I am not familiar with the area so I have no idea whether this is the
right way to go but after applying this patch the problem is not
reproducible anymore.
If the patch is correct then please mark it for stable (3.7+).

Thanks!
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