libxc: Fix out-of-memory error handling in xc_cpupool_getinfo()

Avoid freeing info then returning it to the caller.

This is XSA-88.

Coverity-ID: 1056192
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit d883c179a74111a6804baf8cb8224235242a88fc)