drm/i915: Explicit the connector name for DP link training result

This adds the connector name when printing a debug message about the DP
link training result. It is useful to figure out what connector is
failing when multiple DP connectors are used.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@linux.intel.com>
Reviewed-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20170718142536.2306-1-paul.kocialkowski@linux.intel.com