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/gc.c b/fs/f2fs/gc.c
index 332cdfe..81dc017 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -693,7 +693,7 @@
 gc_more:
 	if (unlikely(!(sbi->sb->s_flags & MS_ACTIVE)))
 		goto stop;
-	if (unlikely(is_set_ckpt_flags(F2FS_CKPT(sbi), CP_ERROR_FLAG)))
+	if (unlikely(f2fs_cp_error(sbi)))
 		goto stop;
 
 	if (gc_type == BG_GC && has_not_enough_free_secs(sbi, nfree)) {