f2fs: support discard submission error injection

This patch adds to support discard submission error injection for testing
error handling of __submit_discard_cmd().

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index bd57be4..30bd913 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -55,6 +55,7 @@ char *f2fs_fault_name[FAULT_MAX] = {
 	[FAULT_TRUNCATE]	= "truncate fail",
 	[FAULT_IO]		= "IO error",
 	[FAULT_CHECKPOINT]	= "checkpoint error",
+	[FAULT_DISCARD]		= "discard error",
 };
 
 void f2fs_build_fault_attr(struct f2fs_sb_info *sbi, unsigned int rate)