channel-main: Don't use SPICE_CHANNEL if not necessary

src_channel and dst_channel are already SpiceChannel*.

Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
2 jobs for mr_convert in 2 minutes and 30 seconds
latest
Status Job ID Name Coverage
  Test
passed #5139102
fedora

00:02:30

passed #5139103
windows

00:02:12