drm/i915/bxt: Use PHY0 GRC value for HW state verification

It's possible that BIOS enables PHY1 only to read out the GRC value from
it to be used in PHY0 and then disables PHY1. In this case we can't use
the PHY1 GRC value for state verification, so use instead the one in PHY0
always.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461174366-16758-2-git-send-email-imre.deak@intel.com