scd: Fix Cherry ST-2000 support for pinpad input.

[NIIBE Yutaka]

Hello,

I applied and push a patch to fix an issue of pinpad input support for
Cherry ST-2000.

I saw two issues (2003 and 2004) in the BTS and a report in
gnupg-users.

I believe that in-stock CCID driver works fine with this patch.  I'm
not sure if the change is enough for PC/SC service on Windows.

For GNU/Linux, I recommend in-stock CCID driver.
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