Fix thinko with definition of REINDEXOPT_MISSING_OK

This had no direct consequences, but let's be consistent and it would be
confusing when adding new flags.  Oversight in 1d654166.

Reported-by: Justin Pryzby
Discussion: https://postgr.es/m/20200902024148.GB20149@telsasoft.com

src/include/nodes/parsenodes.h

@@ -3352,7 +3352,7 @@ typedef struct ConstraintsSetStmt
 /* Reindex options */
 #define REINDEXOPT_VERBOSE (1 << 0) /* print progress info */
 #define REINDEXOPT_REPORT_PROGRESS (1 << 1) /* report pgstat progress */
-#define REINDEXOPT_MISSING_OK (2 << 1)	/* skip missing relations */
+#define REINDEXOPT_MISSING_OK (1 << 2)	/* skip missing relations */
 
 typedef enum ReindexObjectType
 {