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: d555cb5827 ("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>

drivers/gpu/drm/i915/intel_pm.c

@@ -4459,8 +4459,8 @@ static int skl_compute_plane_wm(const struct drm_i915_private *dev_priv,
 		if ((cpp * cstate->base.adjusted_mode.crtc_htotal / 512 < 1) &&
 		    (plane_bytes_per_line / 512 < 1))
 			selected_result = method2;
-		else if ((ddb_allocation && ddb_allocation /
-			fixed16_to_u32_round_up(plane_blocks_per_line)) >= 1)
+		else if (ddb_allocation >=
+			 fixed16_to_u32_round_up(plane_blocks_per_line))
 			selected_result = min_fixed16(method1, method2);
 		else if (latency >= linetime_us)
 			selected_result = min_fixed16(method1, method2);