staging: ccree: handle end of sg list gracefully

If we are asked for number of entries of an offset bigger than the
sg list we should not crash.

Cc: stable@vger.kernel.org
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>