[stable 4.3] drm/nouveau/pmu: do not assume a PMU is present

[Ben Hutchings <ben@xxxxxxxxxxxxxxx>]

Please pick this commit for 4.3-stable:

commit 579b7c58215329803ce184704463de09f0f310ac
Author: Alexandre Courbot <acourbot@xxxxxxxxxx>
Date:   Thu Sep 3 17:39:52 2015 +0900

    drm/nouveau/pmu: do not assume a PMU is present
    
    Some devices may not have a PMU. Avoid a NULL pointer dereference in
    such cases by checking whether the pointer given to nvkm_pmu_pgob() is
    valid.
    
    Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
    Signed-off-by: Ben Skeggs <bskeggs@xxxxxxxxxx>

Ben

-- 
Ben Hutchings
All the simple programs have been written, and all the good names taken.

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