channel: Move local variables to inner block
channel: Move local variables to inner block

Less things to keep track of when taking a quick look at the code flow
of the spice_channel_load_ca() method.

Signed-off-by: Christophe Fergeau <05b95054a663c388a4e33d95828cb30f0370f8ef@redhat.com>

fgouget/spice-gtk,fgouget/spice-gtk,fgouget/spice-gtk,flexVDI/spice-gtk,flexVDI/spice-gtk