drm/amdgpu: Declare Unpin BO api as static

Fixes warning report from kernel test robot
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Ramesh Errabolu <Ramesh.Errabolu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c

@@ -1326,7 +1326,7 @@ static int amdgpu_amdkfd_gpuvm_pin_bo(struct amdgpu_bo *bo, u32 domain)
  *   - All other BO types (GTT, VRAM, MMIO and DOORBELL) will have their
  *     PIN count decremented. Calls to UNPIN must balance calls to PIN
  */
-void amdgpu_amdkfd_gpuvm_unpin_bo(struct amdgpu_bo *bo)
+static void amdgpu_amdkfd_gpuvm_unpin_bo(struct amdgpu_bo *bo)
 {
 	int ret = 0;