libxenevtchn: rename evtchn_port_or_errot_t as xenevtchn_port...

libxenevtchn: rename evtchn_port_or_errot_t as xenevtchn_port...

Otherwise the name clashes with the libxc evtchn_compat use of the
name (which is compat, so can't really change), and triggers an error
with older gcc relating to redefining typedefs (which are not allowed
per the spec, but which are tolerated by newer gcc)

None of qemu-trad, qemu-xen or mini-os actually use this type, so this
should be fine. Note that the library API is not actually stable until
4.7 is releases.

Reported-by: Olaf Hering <olaf@aepfle.de>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Tested-by: Olaf Hering <olaf@aepfle.de>
Acked-by: Wei Liu <wei.liu2@citrix.com>