drm/amd/display: fix non-kernel-doc comment warnings

Fix kernel-doc warnings for a comment that should not use
kernel-doc notation:

dmub_psr.c:235: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 * Set PSR power optimization flags.
dmub_psr.c:235: warning: missing initial short description on line:
 * Set PSR power optimization flags.

Fixes: e5dfcd27 ("drm/amd/display: dc_link_set_psr_allow_active refactoring")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: kernel test robot <lkp@intel.com>
Cc: Robin Chen <po-tchen@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Anthony Koo <Anthony.Koo@amd.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
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>