commit 33baefe5 upstream.

krealloc() doesn't work always properly with __GFP_ZERO flag as
expected.  For clearing the reallocated area, we need to clear
explicitly instead.
Reported-by: Joe Perches <joe@perches.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
[bwh: Backported to 3.16: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>