qcow2: fix wrong value of L1E_OFFSET_MASK, L2E_OFFSET_MASK and REFT_OFFSET_MASK

Accoring to qcow spec, the offset fields in l1e, l2e and ref table entry
start at bit 9. The offset is cluster offset, and the smallest possible
cluster size is 512 bytes.
Signed-off-by: NHu Tao <hutao@cn.fujitsu.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/qcow2.h

@@ -340,11 +340,11 @@ typedef enum QCow2MetadataOverlap {
 #define QCOW2_OL_ALL \
     (QCOW2_OL_CACHED | QCOW2_OL_INACTIVE_L2)
 
-#define L1E_OFFSET_MASK 0x00ffffffffffff00ULL
-#define L2E_OFFSET_MASK 0x00ffffffffffff00ULL
+#define L1E_OFFSET_MASK 0x00fffffffffffe00ULL
+#define L2E_OFFSET_MASK 0x00fffffffffffe00ULL
 #define L2E_COMPRESSED_OFFSET_SIZE_MASK 0x3fffffffffffffffULL
 
-#define REFT_OFFSET_MASK 0xffffffffffffff00ULL
+#define REFT_OFFSET_MASK 0xfffffffffffffe00ULL
 
 static inline int64_t start_of_cluster(BDRVQcowState *s, int64_t offset)
 {