drm/i915: Fix for_each_intel_plane_mask definition

Using for_each_intel_plane_mask() fails because of an extra bracket,
remove the bracket so we can use it in the next commit.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004113514.17064-3-maarten.lankhorst@linux.intel.com


Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>