migration: Plug memory leak with migration URIs

migration: Plug memory leak with migration URIs

migrate_uri_parse() allocates memory to 'channel' if the user
opts for old syntax - uri, which is leaked because there is no
code for freeing 'channel'.
So, free channel to avoid memory leak in case where 'channels'
is empty and uri parsing is required.

Fixes: 5994024f ("migration: Implement MigrateChannelList to qmp migration flow")
Signed-off-by: Het Gala <het.gala@nutanix.com>
Suggested-by: Markus Armbruster <armbru@redhat.com>
Tested-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Link: https://lore.kernel.org/r/20231129204301.131228-1-het.gala@nutanix.com
Signed-off-by: Peter Xu <peterx@redhat.com>