qapi-schema: fix typo about change-vnc-password

Signed-off-by: NGonglei <arei.gonglei@huawei.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMichael Tokarev <mjt@tls.msk.ru>

qapi-schema.json

@@ -1533,7 +1533,7 @@
 #
 # Change the VNC server password.
 #
-# @target:  the new password to use with VNC authentication
+# @password:  the new password to use with VNC authentication
 #
 # Since: 1.1
 #