Commit 58760cc3dd94 ("Add XENBUS_SHARED_INFO method to check whether event
upcalls are supported") added a new version of the XENBUS_SHARED_INFO
interface but there was a typo in the line added into revisions.h and hence
the XENBUS PDO revision was left as 0x09000008 rather then being increased to
0x09000009. This patch rectifies the situation.