drm/amdgpu: retire unused get_umc_v6_7_channel_index

Fix the following compile warning:

drivers/gpu/drm/amd/amdgpu/umc_v6_7.c:53:24: warning: unused function 'get_umc_v6_7_channel_index' [-Wunused-function]
static inline uint32_t get_umc_v6_7_channel_index(struct amdgpu_device *adev,
                          ^
1 warning generated.
Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/umc_v6_7.c

@@ -57,13 +57,6 @@ static inline uint32_t get_umc_v6_7_reg_offset(struct amdgpu_device *adev,
 	return adev->umc.channel_offs * ch_inst + UMC_V6_7_INST_DIST * umc_inst;
 }
 
-static inline uint32_t get_umc_v6_7_channel_index(struct amdgpu_device *adev,
-					      uint32_t umc_inst,
-					      uint32_t ch_inst)
-{
-	return adev->umc.channel_idx_tbl[umc_inst * adev->umc.channel_inst_num + ch_inst];
-}
-
 static void umc_v6_7_query_error_status_helper(struct amdgpu_device *adev,
 						  uint64_t mc_umc_status, uint32_t umc_reg_offset)
 {