f2fs: return a default value for non-void function

This patch resolves a build warning reported by kbuild test robot.

"
fs/f2fs/segment.c: In function '__get_segment_type':
fs/f2fs/segment.c:806:1: warning: control reaches end of non-void
function [-Wreturn-type]
"

Signed-off-by: Jaegeuk Kim <[email protected]>
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index ca7b5ff..fe2cc0b 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -791,11 +791,10 @@
 		return __get_segment_type_2(page, p_type);
 	case 4:
 		return __get_segment_type_4(page, p_type);
-	case 6:
-		return __get_segment_type_6(page, p_type);
-	default:
-		BUG();
 	}
+	/* NR_CURSEG_TYPE(6) logs by default */
+	BUG_ON(sbi->active_logs != NR_CURSEG_TYPE);
+	return __get_segment_type_6(page, p_type);
 }
 
 static void do_write_page(struct f2fs_sb_info *sbi, struct page *page,