drm/sti: remove extra mode fixup

Commit 652353e6 ("drm/sti: set CRTC
modesetting parameters") added a hack to avoid warnings related to
setting mode with atomic API. With the previous patch, the hack should
no longer be necessary.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Vincent Abriou <vincent.abriou@st.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>