drm/i915/tgl/dsi: Do not override TA_SURE

Do not override TA_SURE timing parameter to
zero for DSI 8X frequency 800MHz or below on
TGL.

Signed-off-by: Vandita Kulkarni <vandita.kulkarni@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190730073648.5157-4-vandita.kulkarni@intel.com