erofs: use poison pointer to replace the hard-coded address

It's safer and cleaner to replace such hard-coded illegal pointer
with poison pointers.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Link: https://lore.kernel.org/r/20230526201459.128169-7-hsiangkao@linux.alibaba.com

fs/erofs/zdata.c

@@ -91,10 +91,8 @@ struct z_erofs_pcluster {
 	struct z_erofs_bvec compressed_bvecs[];
 };
 
-/* let's avoid the valid 32-bit kernel addresses */
-
 /* the end of a chain of pclusters */
-#define Z_EROFS_PCLUSTER_TAIL           ((void *)0x5F0ECAFE)
+#define Z_EROFS_PCLUSTER_TAIL           ((void *) 0x700 + POISON_POINTER_DELTA)
 #define Z_EROFS_PCLUSTER_NIL            (NULL)
 
 struct z_erofs_decompressqueue {