drm/amdgpu: remove unused variable

building with gcc and W=1 reports
drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c:7292:11: error:
unused variable 'tmp' [-Werror=unused-variable]
  uint32_t tmp;
           ^~~

tmp is not used so remove it.
Signed-off-by: bobzhou <bob.zhou@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c

@@ -7266,7 +7266,6 @@ static int gfx_v10_0_hw_fini(void *handle)
 {
 	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
 	int r;
-	uint32_t tmp;
 
 	amdgpu_irq_put(adev, &adev->gfx.priv_reg_irq, 0);
 	amdgpu_irq_put(adev, &adev->gfx.priv_inst_irq, 0);