drm/amdgpu: remove set but not used variable 'ring'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/amd/amdgpu/psp_v10_0.c: In function 'psp_v10_0_ring_stop':
drivers/gpu/drm/amd/amdgpu/psp_v10_0.c:230:19: warning:
 variable 'ring' set but not used [-Wunused-but-set-variable]

drivers/gpu/drm/amd/amdgpu/psp_v3_1.c: In function 'psp_v3_1_ring_stop':
drivers/gpu/drm/amd/amdgpu/psp_v3_1.c:359:19: warning:
 variable ‘ring’ set but not used [-Wunused-but-set-variable]

It not used since commit
4ef72453 ("drm/amdgpu: added api for stopping psp ring (v2)")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/psp_v10_0.c

@@ -240,12 +240,9 @@ static int psp_v10_0_ring_stop(struct psp_context *psp,
 			       enum psp_ring_type ring_type)
 {
 	int ret = 0;
-	struct psp_ring *ring;
 	unsigned int psp_ring_reg = 0;
 	struct amdgpu_device *adev = psp->adev;
 
-	ring = &psp->km_ring;
-
 	/* Write the ring destroy command to C2PMSG_64 */
 	psp_ring_reg = 3 << 16;
 	WREG32_SOC15(MP0, 0, mmMP0_SMN_C2PMSG_64, psp_ring_reg);

drivers/gpu/drm/amd/amdgpu/psp_v3_1.c

@@ -356,12 +356,9 @@ static int psp_v3_1_ring_stop(struct psp_context *psp,
 			      enum psp_ring_type ring_type)
 {
 	int ret = 0;
-	struct psp_ring *ring;
 	unsigned int psp_ring_reg = 0;
 	struct amdgpu_device *adev = psp->adev;
 
-	ring = &psp->km_ring;
-
 	/* Write the ring destroy command to C2PMSG_64 */
 	psp_ring_reg = 3 << 16;
 	WREG32_SOC15(MP0, 0, mmMP0_SMN_C2PMSG_64, psp_ring_reg);