[8u] RFR: 8250875: Incorrect parameter type for update_number in JDK_Version::jdk_update

[Denghui Dong]

Hi,
Could I have a review of this trivial fix that amend the type of update_number in JDK_Version::jdk_update?
Summary:
Now the update number is over 255, and if we make some flags obsolete later,
it will cause a build failure

Bug: https://bugs.openjdk.java.net/browse/JDK-8250875
Webrev: http://cr.openjdk.java.net/~ddong/8250875/webrev.00/

Thanks
Denghui Dong