sc_helpers: shrinken allocated buffer
sc_helpers: shrinken allocated buffer

There is no need to allocate 512-bytes buffer. 256 + 2 (data + SW) is enough.

Signed-off-by: Dmitry Eremin-Solenikov <b6edad08270b2e4ffbcb0879e25a0e29a48c5275@gmail.com>

lumag/emv-tools