char: pcmcia: error out if 'num_bytes_read' is greater than 4 in set_protocol()

Theoretically, it will cause index out of bounds error if
'num_bytes_read' is greater than 4. As we expect it(and was tested)
never to be greater than 4, error out if it happens.

Fixes: c1986ee9

 ("[PATCH] New Omnikey Cardman 4000 driver")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Link: https://lore.kernel.org/r/20210521120617.138396-1-yukuai3@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>