drm/amd/display: clean up dcn32_fpu.c kernel-doc

Rectify multiple kernel-doc warnings in dcn32_fpu.c.
E.g.:

drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/dcn32_fpu.c:247: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
    * Finds dummy_latency_index when MCLK switching using firmware based
drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/dcn32_fpu.c:484: warning: Function parameter or member 'phantom_stream' not described in 'dcn32_set_phantom_stream_timing'
drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/dcn32_fpu.c:601: warning: Function parameter or member 'dc' not described in 'dcn32_assign_subvp_pipe'
drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/dcn32_fpu.c:601: warning: Function parameter or member 'context' not described in 'dcn32_assign_subvp_pipe'
drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/dcn32_fpu.c:601: warning: Function parameter or member 'index' not described in 'dcn32_assign_subvp_pipe'
drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/dcn32_fpu.c:2140: warning: Function parameter or member 'dc' not described in 'dcn32_update_bw_bounding_box_fpu'
drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/dcn32_fpu.c:2140: warning: Function parameter or member 'bw_params' not described in 'dcn32_update_bw_bounding_box_fpu'
drivers/gpu/drm/amd/amdgpu/../display/dc/dml/dcn32/dcn32_fpu.c:2140: warning: expecting prototype for dcn32_update_bw_bounding_box(). Prototype was for dcn32_update_bw_bounding_box_fpu() instead
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: George Shen <george.shen@amd.com>
Cc: Alvin Lee <alvin.lee2@amd.com>
Cc: Nevenko Stupar <Nevenko.Stupar@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>