drm/i915: Fix bad comparison in skl_compute_plane_wm, v2.

drm/i915: Fix bad comparison in skl_compute_plane_wm, v2.

ddb_allocation && ddb_allocation / blocks_per_line >= 1 is the same
as ddb_allocation >= blocks_per_line, so use the latter to simplify
this.

This fixes the following compiler warning:

drivers/gpu/drm/i915/intel_pm.c:4467]: (warning) Comparison of a
boolean expression with an integer other than 0 or 1.

Changes since v1:
- Rebase, was missing the changes to the macro names.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: 6d828071d28e ("drm/i915/skl+: use linetime latency if ddb size is not available")
Cc: "Mahesh Kumar" <mahesh1.kumar@intel.com>
Reported-by: David Binderman <dcb314@hotmail.com>
Cc: David Binderman <dcb314@hotmail.com>
Cc: <drm-intel-fixes@lists.freedesktop.org> # v4.13-rc1+
Link: http://patchwork.freedesktop.org/patch/msgid/20170717120230.2023-1-maarten.lankhorst@linux.intel.com
Reviewed-by: Mahesh Kumar <mahesh1.kumar@intel.com>