Fix integer overflow in block migration bandwidth calculation

block_mig_state.reads is an int, and multiplying by BLOCK_SIZE yielded a
negative number, resulting in a negative bandwidth (running on a 32-bit
machine).  Change order to avoid.
Signed-off-by: NAvishay Traeger <avishay@il.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block-migration.c

@@ -140,7 +140,7 @@ static inline void add_avg_read_time(int64_t time)
 static inline long double compute_read_bwidth(void)
 {
     assert(block_mig_state.total_time != 0);
-    return  (block_mig_state.reads * BLOCK_SIZE)/ block_mig_state.total_time;
+    return (block_mig_state.reads / block_mig_state.total_time) * BLOCK_SIZE;
 }
 
 static int bmds_aio_inflight(BlkMigDevState *bmds, int64_t sector)