Pull xen fixes from Juergen Gross:
"Just two small fixes for the new pvcalls frontend driver"
* tag 'for-linus-4.15-rc3-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip:
xen/pvcalls: Fix a check in pvcalls_front_remove()
xen/pvcalls: check for xenbus_read() errors