hw/isa/superio: Fix inconsistent use of Chardev->be

hw/isa/superio: Fix inconsistent use of Chardev->be

4c3119a6e3e and cd9526ab7c0 introduced an incorrect and inconsistent
use of Chardev->be. Also, this CharBackend member is private and is
not supposed to be accessible.

Fix it by removing the inconsistent check.

Cc: qemu-stable@nongnu.org
Reported-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180515152500.19460-2-f4bug@amsat.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
(cherry picked from commit d4c8fcd91abba584f2788dfe5fba5245cea380f0)
 Conflicts:
	hw/isa/isa-superio.c
* avoid context dep on 9bca0edb28
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>