drm/i915: Fix port name in vlv_wait_port_ready() timeout warning

We're currently misprinting the port name when vlv_wait_port_ready()
times out. Fix it by using port_name().

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>