sandbox: tpm: Fix nvwrite command

The original codes misused recvbuf in source buffer instead of sendbuf,
and read from incorrect offset 14 instead of 22.

Signed-off-by: Che-Liang Chiou <clchiou@chromium.org>

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Che-Liang Chiou <clchiou@chromium.org>