drm/i915/dp_mst: Use link.{min/max}_bpp_x16

The link.{min/max}_bpp_x16 is already set in crtc_state, use that while
computing link config for MST.

Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241217093244.3938132-15-ankit.k.nautiyal@intel.com