Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega12_thermal.c:63: warning: Cannot understand  * @fn vega12_enable_fan_control_feature
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega12_thermal.c:137: warning: Function parameter or member 'hwmgr' not described in 'vega12_fan_ctrl_reset_fan_speed_to_default'
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega12_thermal.c:147: warning: Function parameter or member 'hwmgr' not described in 'vega12_thermal_get_temperature'
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega12_thermal.c:172: warning: Function parameter or member 'hwmgr' not described in 'vega12_thermal_set_temperature_range'
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega12_thermal.c:172: warning: Function parameter or member 'range' not described in 'vega12_thermal_set_temperature_range'
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega12_thermal.c:208: warning: Function parameter or member 'hwmgr' not described in 'vega12_thermal_enable_alert'
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega12_thermal.c:226: warning: Function parameter or member 'hwmgr' not described in 'vega12_thermal_disable_alert'
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega12_thermal.c:240: warning: Function parameter or member 'hwmgr' not described in 'vega12_thermal_stop_thermal_controller'
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega12_thermal.c:256: warning: Function parameter or member 'hwmgr' not described in 'vega12_thermal_setup_fan_table'
 drivers/gpu/drm/amd/amdgpu/../pm/powerplay/hwmgr/vega12_thermal.c:279: warning: Function parameter or member 'hwmgr' not described in 'vega12_thermal_start_smc_fan_control'

Cc: Evan Quan <evan.quan@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>