drm/i915/gen10: fix WM latency printing

Gen 10 is just like Gen 9, so let's consider that all the future
platforms are going to be like gen 9 instead of being like gen8-.

Cc: Mahesh Kumar <mahesh1.kumar@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170809205248.11917-4-rodrigo.vivi@intel.com