libxc: Only retry mapping pages when ENOENT is returned

libxc: Only retry mapping pages when ENOENT is returned

If the return value from the ioctl() is not ENOENT, it's possible that err[i]
will not be updated and libxc will just loop forever.  Although it's unlikely
that err[i] would not be updated after the ioctl() gets through at least once,
it's better to be defensive.

Signed-off-by: Adin Scannell <adin@scannell.ca>
Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>