drm: fix typo in comment

Fix typo in a doxygen comment (replaced green by blue) in drm_color_mgmt.c

Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220426131912.3850354-1-raphael.gallais-pou@foss.st.com