f2fs: support IO error injection

This patch adds to support IO error injection for testing IO error
tolerance of f2fs.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -50,6 +50,7 @@ char *fault_name[FAULT_MAX] = {
 	[FAULT_BLOCK]		= "no more block",
 	[FAULT_DIR_DEPTH]	= "too big dir depth",
 	[FAULT_EVICT_INODE]	= "evict_inode fail",
+	[FAULT_IO]		= "IO error",
 };
 
 static void f2fs_build_fault_attr(unsigned int rate)