drm/amdgpu: Fix double free of dmabuf

amdgpu_amdkfd_gpuvm_free_memory_of_gpu drop dmabuf reference increased in
amdgpu_gem_prime_export.
amdgpu_bo_destroy drop dmabuf reference increased in
amdgpu_gem_prime_import.

So remove this extra dma_buf_put to avoid double free.

Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Tested-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>