tcti: spi helper check size
tcti: spi helper check size

Verify the size of the tcti buffer is not too small to dereference and
use.

Signed-off-by: William Roberts <60148e894dabf0b83bde1d460768794cd453c455@intel.com>

tpm2-software/tpm2-tss,tpm2-software/tpm2-tss,tpm2-software/tpm2-tss