kvazaar: fix build with gcc 7

kvazaar: fix build with gcc 7

Add upstream fix for a gcc 7 -Werror build failure.

Fixes:
http://autobuild.buildroot.net/results/ea1/ea1495696a0e810adb6695dad6b9f3d3363e81d5/
http://autobuild.buildroot.net/results/2c1/2c1fba63553afa735c5ac29d7f5de8368c794628/
http://autobuild.buildroot.net/results/d07/d07bfcb8efcb76cdea3c66e0cc24728f418e3872/

Cc: Alexandre Esse <alexandre.esse.dev@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>