drm/amd/display: fix memory leaks on error exit return

Currently in the case where some of the allocations fail for dce110_tgv,
dce110_xfmv, dce110_miv or dce110_oppv then the exit return path ends
up leaking allocated objects. Fix this by kfree'ing them before returning.
Also re-work the comparison of the null pointers to use the !ptr idiom.

Detected by CoverityScan, CID#1460246, 1460325, 1460324, 1460392
("Resource Leak")

Fixes: c4562236b3bc ("drm/amd/dc: Add dc display driver (v2)")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dce110/dce110_resource.c

@@ -1037,11 +1037,13 @@ static bool underlay_create(struct dc_context *ctx, struct resource_pool *pool)
 	struct dce110_opp *dce110_oppv = kzalloc(sizeof(*dce110_oppv),
 						 GFP_KERNEL);
 
-	if ((dce110_tgv == NULL) ||
-		(dce110_xfmv == NULL) ||
-		(dce110_miv == NULL) ||
-		(dce110_oppv == NULL))
-			return false;
+	if (!dce110_tgv || !dce110_xfmv || !dce110_miv || !dce110_oppv) {
+		kfree(dce110_tgv);
+		kfree(dce110_xfmv);
+		kfree(dce110_miv);
+		kfree(dce110_oppv);
+		return false;
+	}
 
 	dce110_opp_v_construct(dce110_oppv, ctx);