qapi/migration.json: spelling: transfering

Fixes: 074dbce5fcce "migration: New migrate and migrate-incoming argument 'channels'"
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

qapi/migration.json

@@ -1658,7 +1658,7 @@
 #
 # Migration stream channel parameters.
 #
-# @channel-type: Channel type for transfering packet information.
+# @channel-type: Channel type for transferring packet information.
 #
 # @addr: Migration endpoint configuration on destination interface.
 #