sha3: code shrink (and speedup for SHA3_SMALL=0)

function                                             old     new   delta
sha3_process_block72                                1454    1359     -95

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
sha3: tweak comments and indentation

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>