drm/i915/glk: Fix dotclock calculation in skl_check_pipe_max_pixel_rate

drm/i915/glk: Fix dotclock calculation in skl_check_pipe_max_pixel_rate

Seems that GLK has a dotclock that's twice the display clock.
skl_max_scale checks for IS_GEMINILAKE, so perform the same check here.

While at it, change the DRM_ERROR to DEBUG_KMS.

Fixes: 73b0ca8ec76d ("drm/i915/skl+: consider max supported plane pixel
rate while scaling")
Cc: Mahesh Kumar <mahesh1.kumar@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170601103413.7037-1-maarten.lankhorst@linux.intel.com
Reviewed-by: Mahesh Kumar <mahesh1.kumar@intel.com>