amdkfd: properly free gang_ctx_bo when failed to init user queue

In the Linux kernel, the following vulnerability has been resolved:

amdkfd: properly free gang_ctx_bo when failed to init user queue

The destructor of a gtt bo is declared as

void amdgpu_amdkfd_free_gtt_mem(struct amdgpu_device *adev, void **mem_obj);

Which takes void** as the second parameter.

GCC allows passing void* to the function because void* can be implicitly

casted to any other types, so it can pass compiling.

However, passing this void* parameter into the function's

execution process(which expects void** and dereferencing void**)

will result in errors.