qemu-ga: fix confusing GAChannelMethod comparison

In commit 7868e26e5930f49ca942311885776b938dcf3b77
("qemu-ga: add initial win32 support") support was added for qemu-ga on
Windows using virtio-serial.  Other channel methods (ISA serial and UNIX
domain socket) are not supported on Windows.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/channel-win32.c

@@ -287,7 +287,7 @@ GIOStatus ga_channel_write_all(GAChannel *c, const char *buf, size_t size)
 static gboolean ga_channel_open(GAChannel *c, GAChannelMethod method,
                                 const gchar *path)
 {
-    if (!method == GA_CHANNEL_VIRTIO_SERIAL) {
+    if (method != GA_CHANNEL_VIRTIO_SERIAL) {
         g_critical("unsupported communication method");
         return false;
     }