drm/i915/icl: Drop port parameter to icl_get_combo_buf_trans()

The port parameter hasn't been used since the last bspec phy programming
update.  Drop it to make some upcoming changes simpler.

References: 9659c1af ("drm/i915/icl: combo port vswing programming changes per BSPEC")
Cc: Clint Taylor <clinton.a.taylor@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Clint Taylor <Clinton.A.Taylor@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190626000352.31926-2-matthew.d.roper@intel.com