drm/amd/display: DCN3.1: don't mark as kernel-doc

There is no need for this one static function to be marked as
kernel-doc notation.

Avoid this doc build warning:

warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Enable CRTC

Fixes: 110d3968 ("drm/amd/display: Add DCN3.1 OPTC")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: Christian König <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>