amdgpu: Check whether pointer is valid
In amdgpu_bo_cpu_map() check if the caller has set the pointer to a pointer argument named "cpu" before assigning to it.
Sometimes it is useful to use this function to map a bo, without immediately needing its CPU pointer, like this:
res = amdgpu_bo_cpu_map(bo, NULL);
Signed-off-by: Luben Tuikov firstname.lastname@example.org