ubifs: Fix build error without CONFIG_UBIFS_FS_XATTR

Fix gcc build error while CONFIG_UBIFS_FS_XATTR
is not set

fs/ubifs/dir.o: In function `ubifs_unlink':
dir.c:(.text+0x260): undefined reference to `ubifs_purge_xattrs'
fs/ubifs/dir.o: In function `do_rename':
dir.c:(.text+0x1edc): undefined reference to `ubifs_purge_xattrs'
fs/ubifs/dir.o: In function `ubifs_rmdir':
dir.c:(.text+0x2638): undefined reference to `ubifs_purge_xattrs'

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: 9ca2d73 ("ubifs: Limit number of xattrs per inode")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/ubifs.h

@@ -2015,13 +2015,17 @@ int ubifs_xattr_set(struct inode *host, const char *name, const void *value,
 		    size_t size, int flags, bool check_lock);
 ssize_t ubifs_xattr_get(struct inode *host, const char *name, void *buf,
 			size_t size);
-int ubifs_purge_xattrs(struct inode *host);
 
 #ifdef CONFIG_UBIFS_FS_XATTR
 void ubifs_evict_xattr_inode(struct ubifs_info *c, ino_t xattr_inum);
+int ubifs_purge_xattrs(struct inode *host);
 #else
 static inline void ubifs_evict_xattr_inode(struct ubifs_info *c,
 					   ino_t xattr_inum) { }
+static inline int ubifs_purge_xattrs(struct inode *host)
+{
+	return 0;
+}
 #endif
 
 #ifdef CONFIG_UBIFS_FS_SECURITY