Fix bug in transform_neon.c in iSAC codec.

The bug causes AcmReceiverBitExactness and AcmSenderBitExactness test
failed in modules_unittests.

BUG=4002
R=andrew@webrtc.org, jridges@masque.com, kjellander@webrtc.org

Change-Id: I18b00056c53cf4158c186d449e5ab785065cca94

Review URL: https://webrtc-codereview.appspot.com/49889004

Patch from Zhongwei Yao <zhongwei.yao@arm.com>.

Cr-Commit-Position: refs/heads/master@{#9138}
1 file changed