Missed in 870c034d, hopefully reported by Coverity.

Fixes: Coverity CID 1412793 (Incorrect expression)
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20200121213853.9601-1-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>