hw/cxl: Check the length of data requested fits in get_log()

Checking offset + length is of no relevance when verifying the CEL
data will fit in the mailbox payload. Only the length is is relevant.

Note that this removes a potential overflow.

Reported-by: Esifiel <esifiel@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Message-Id: <20241101133917.27634-6-Jonathan.Cameron@huawei.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/cxl/cxl-mailbox-utils.c

@@ -947,7 +947,7 @@ static CXLRetCode cmd_logs_get_log(const struct cxl_cmd *cmd,
      * the only possible failure would be if the mailbox itself isn't big
      * enough.
      */
-    if (get_log->offset + get_log->length > cci->payload_max) {
+    if (get_log->length > cci->payload_max) {
         return CXL_MBOX_INVALID_INPUT;
     }