block: don't use REQ_SYNC in the READ_SYNC definition

Reads are synchronous per definition, don't add another flag for it.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@fb.com>

include/linux/fs.h

@@ -196,7 +196,7 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 #define READ			REQ_OP_READ
 #define WRITE			REQ_OP_WRITE
 
-#define READ_SYNC		REQ_SYNC
+#define READ_SYNC		0
 #define WRITE_SYNC		(REQ_SYNC | REQ_NOIDLE)
 #define WRITE_ODIRECT		REQ_SYNC
 #define WRITE_FLUSH		(REQ_SYNC | REQ_NOIDLE | REQ_PREFLUSH)