scd: Fix memory leak in ccid-driver.

* scd/ccid-driver.c (ccid_dev_scan): Use loop var and not the count.

Due to an assignment out of bounds this might lead to a crash if there
are more than 15 readers. In any case it fixes a memory leak.
Kudos to the friendly auditor who found that bug.

• Fixes-commit: 8a41e73c31adb86d4a7dca4da695e5ad1347811f