drm/i915/dp: Rename intel_ddi_disable_fec_state() to intel_ddi_disable_fec()

Rename intel_ddi_disable_fec_state() to intel_ddi_disable_fec(), for
symmetry with intel_ddi_enable_fec().

Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231030155843.2251023-19-imre.deak@intel.com