drm/amdgpu: Remove unused get_umc_v8_7_channel_index function

Remove get_umc_v8_7_channel_index function, which is not used
in the codebase.

This was pointed by clang with the following warning:

drivers/gpu/drm/amd/amdgpu/umc_v8_7.c:50:24: warning: unused function
'get_umc_v8_7_channel_index' [-Wunused-function]
static inline uint32_t get_umc_v8_7_channel_index(struct amdgpu_device *adev,
                       ^
Signed-off-by: Maíra Canal <maira.canal@usp.br>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/umc_v8_7.c

@@ -47,13 +47,6 @@ static inline uint32_t get_umc_v8_7_reg_offset(struct amdgpu_device *adev,
 	return adev->umc.channel_offs*ch_inst + UMC_8_INST_DIST*umc_inst;
 }
 
-static inline uint32_t get_umc_v8_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_v8_7_ecc_info_query_correctable_error_count(struct amdgpu_device *adev,
 						uint32_t umc_inst, uint32_t ch_inst,
 						unsigned long *error_count)