minor malloc changes

replace malloc + memset with calloc since calloc may skip the memset if
returned memory comes directly from sbrk()

use malloc instead of malloc if first thing done with allocated memory is
to flip all bits to 1.

Signed-off-by: Olivier Langlois <olivier@trillion01.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>