Use case-scope error labels handling LTTNG_CONSUMER_ROTATE_CHANNEL

This cleans-up the error handling of the case handling the
LTTNG_CONSUMER_ROTATE_CHANNEL command. This is done in order to allow
a follow-up commit to perform some common clean-up operations on error
while introducing as few changes as possible.

No behaviour change is intended.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>