drm/amd/display: Address kdoc for 'Enable CRTC' in optc401_enable_crtc

This commit fixes the kdoc for 'Enable CRTC' in `optc401_enable_crtc`
function.

Fixes the below with gcc W=1:
drivers/gpu/drm/amd/amdgpu/../display/dc/optc/dcn401/dcn401_optc.c:177: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Enable CRTC

Fixes: 70839da6 ("drm/amd/display: Add new DCN401 sources")
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Roman Li <roman.li@amd.com>
Cc: Qingqing Zhuo <Qingqing.Zhuo@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>