vmdk: Widen before shifting 32 bit header field

Coverity spotted this.

The field is 32 bits, but if it's possible to overflow in 32 bit
left shift.
Signed-off-by: NFam Zheng <famz@redhat.com>
Reviewed-by: NJohn Snow <jsnow@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/vmdk.c

@@ -523,7 +523,7 @@ static int vmdk_open_vmfs_sparse(BlockDriverState *bs,
     }
     ret = vmdk_add_extent(bs, file, false,
                           le32_to_cpu(header.disk_sectors),
-                          le32_to_cpu(header.l1dir_offset) << 9,
+                          (int64_t)le32_to_cpu(header.l1dir_offset) << 9,
                           0,
                           le32_to_cpu(header.l1dir_size),
                           4096,