Commit b606bbb4 broke reporting of errors when setting of guest time
fails via the guest agent as the return value is not checked and later
overwritten by the return value qemuMonitorRTCResetReinjection();

Fix this by checking the return value before resetting the RTC
reinjection.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1142294