ubifs: Fix build errors as symbol undefined

With CONFIG_UBIFS_FS_AUTHENTICATION not set, the compiler can assume that
ubifs_node_check_hash() is never true and drops the call to ubifs_bad_hash().
Is CONFIG_CC_OPTIMIZE_FOR_SIZE enabled this optimization does not happen anymore.

So When CONFIG_UBIFS_FS and CONFIG_CC_OPTIMIZE_FOR_SIZE is enabled but
CONFIG_UBIFS_FS_AUTHENTICATION is not set, the build errors is as followd:
    ERROR: modpost: "ubifs_bad_hash" [fs/ubifs/ubifs.ko] undefined!

Fix it by add no-op ubifs_bad_hash() for the CONFIG_UBIFS_FS_AUTHENTICATION=n case.

Fixes: 16a26b20 ("ubifs: authentication: Add hashes to index nodes")
Signed-off-by: Li Hua <hucool.lihua@huawei.com>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/ubifs.h

@@ -1623,8 +1623,13 @@ static inline int ubifs_check_hmac(const struct ubifs_info *c,
 	return crypto_memneq(expected, got, c->hmac_desc_len);
 }
 
+#ifdef CONFIG_UBIFS_FS_AUTHENTICATION
 void ubifs_bad_hash(const struct ubifs_info *c, const void *node,
 		    const u8 *hash, int lnum, int offs);
+#else
+static inline void ubifs_bad_hash(const struct ubifs_info *c, const void *node,
+				  const u8 *hash, int lnum, int offs) {};
+#endif
 
 int __ubifs_node_check_hash(const struct ubifs_info *c, const void *buf,
 			  const u8 *expected);