hw/cxl: Fix uint32 overflow cxl-mailbox-utils.c

hw/cxl: Fix uint32 overflow cxl-mailbox-utils.c

The sum offset + length may overflow uint32. Since this sum is
compared with uint64_t return value of get_lsa_size(), it makes
sense to choose uint64_t type for offset and length.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 3ebe676a3463 ("hw/cxl/device: Implement get/set Label Storage Area (LSA)")
Signed-off-by: Dmitry Frolov <frolov@swemel.ru>
Link: https://lore.kernel.org/r/20240917080925.270597-2-frolov@swemel.ru
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-Id: <20241014121902.2146424-2-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>