drm/amd/display: Adjust kdoc for 'dcn35_hw_block_power_down' & 'dcn35_hw_block_power_up'

Fixes the following gcc with W=1:

drivers/gpu/drm/amd/amdgpu/../display/dc/hwss/dcn35/dcn35_hwseq.c:1124: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

Cc: Charlene Liu <charlene.liu@amd.com>
Cc: Muhammad Ahmed <ahmed.ahmed@amd.com>
Cc: Hamza Mahfooz <hamza.mahfooz@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Srinath Rao <srinath.rao@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>