drm/i915/skl+: no need to memset again

We are already doing memset of ddb structure at the begining of skl_allocate_pipe_ddb
function, No need to again do a memset.

Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170517115831.13830-7-mahesh1.kumar@intel.com