There is no point in looking for a 48-bit opcode if we've
not read the second word for a 32-bit opcode.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20221106023735.5277-5-richard.henderson@linaro.org>