f2fs: introduce f2fs_cp_error for readability

This patch adds f2fs_cp_error for readability.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index e161e13..8aabe3e 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -815,7 +815,7 @@
 	if (unlikely(fsmeta >= total))
 		return 1;
 
-	if (unlikely(is_set_ckpt_flags(ckpt, CP_ERROR_FLAG))) {
+	if (unlikely(f2fs_cp_error(sbi))) {
 		f2fs_msg(sbi->sb, KERN_ERR, "A bug case: need to run fsck");
 		return 1;
 	}