drm/amdgpu: remove structurally dead code for amd_gmc

This code cannot be reached: return sysfs_emit(buf, "UNK....)
Signed-off-by: Jesse Zhang <Jesse.Zhang@amd.com>
Reviewed-by: Tim Huang <Tim.Huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1148,8 +1148,6 @@ static ssize_t current_memory_partition_show(
 	default:
 		return sysfs_emit(buf, "UNKNOWN\n");
 	}
-
-	return sysfs_emit(buf, "UNKNOWN\n");
 }
 
 static DEVICE_ATTR_RO(current_memory_partition);