drm/sti: Drop bogus drm_mode_sort() call

sti seems confused about which mode list is used in its .get_modes()
hook. It adds the modes to the probed_modes list (as is appropriate)
but then for some reason it tries to sort the old mode list.

Just drop the sorting since it does nothing, and let the probe helper
do its thing. It will sort the final mode list after merging in the
modes from the probed_modes list and validating them.

Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Vincent Abriou <vincent.abriou@st.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1449177255-9515-8-git-send-email-ville.syrjala@linux.intel.com