drm/amdgpu/vcn:Fix uninitialized symbol error

ret_code should be initialized with 0. The check of read/write
ptr should be activate when UVD_POWER_STATUS_TILES is off.
Signed-off-by: James Zhu <James.Zhu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/vcn_v1_0.c

@@ -1165,14 +1165,14 @@ static int vcn_v1_0_stop_spg_mode(struct amdgpu_device *adev)
 
 static int vcn_v1_0_stop_dpg_mode(struct amdgpu_device *adev)
 {
-	int ret_code;
+	int ret_code = 0;
 
 	/* Wait for power status to be UVD_POWER_STATUS__UVD_POWER_STATUS_TILES_OFF */
 	SOC15_WAIT_ON_RREG(UVD, 0, mmUVD_POWER_STATUS,
 			UVD_POWER_STATUS__UVD_POWER_STATUS_TILES_OFF,
 			UVD_POWER_STATUS__UVD_POWER_STATUS_MASK, ret_code);
 
-	if (ret_code) {
+	if (!ret_code) {
 		int tmp = RREG32_SOC15(UVD, 0, mmUVD_RBC_RB_WPTR) & 0x7FFFFFFF;
 		/* wait for read ptr to be equal to write ptr */
 		SOC15_WAIT_ON_RREG(UVD, 0, mmUVD_RBC_RB_RPTR, tmp, 0xFFFFFFFF, ret_code);