drm/omap: fix possible NULL ref issue in tiler_reserve_2d

tiler_reserve_2d allocates memory but does not check if it got the
memory. Add the check and return ENOMEM on failure.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180329104038.29154-2-tomi.valkeinen@ti.comReviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

drivers/gpu/drm/omapdrm/omap_dmm_tiler.c

@@ -401,12 +401,16 @@ int tiler_unpin(struct tiler_block *block)
 struct tiler_block *tiler_reserve_2d(enum tiler_fmt fmt, u16 w,
 		u16 h, u16 align)
 {
-	struct tiler_block *block = kzalloc(sizeof(*block), GFP_KERNEL);
+	struct tiler_block *block;
 	u32 min_align = 128;
 	int ret;
 	unsigned long flags;
 	u32 slot_bytes;
 
+	block = kzalloc(sizeof(*block), GFP_KERNEL);
+	if (!block)
+		return ERR_PTR(-ENOMEM);
+
 	BUG_ON(!validfmt(fmt));
 
 	/* convert width/height to slots */