drm/amdkfd: Fix NULL pointer dereference

Check that adev->gfx.ras is valid before using it.

Fixes: 6475ae2b ("drm/amdgpu: add UTCL2 RAS poison query for Aldebaran (v2)")
CC: Tao Zhou <tao.zhou1@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Mukul Joshi <mukul.joshi@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -727,7 +727,7 @@ void amdgpu_amdkfd_ras_poison_consumption_handler(struct amdgpu_device *adev, bo
 
 bool amdgpu_amdkfd_ras_query_utcl2_poison_status(struct amdgpu_device *adev)
 {
-	if (adev->gfx.ras->query_utcl2_poison_status)
+	if (adev->gfx.ras && adev->gfx.ras->query_utcl2_poison_status)
 		return adev->gfx.ras->query_utcl2_poison_status(adev);
 	else
 		return false;