Refactor audio_coding/codecs/isac/fix: Removed usage of trivial macro WEBRTC_SPL_LSHIFT_W32()

The macro is defined as
#define WEBRTC_SPL_LSHIFT_W32(a, b) ((a) << (b))
hence trivial.
The macro name may in fact mislead the user to assume a cast/truncation to int32_t is done.
- Removing usage of it.
- Some style changes.

BUG=3348, 3353
TESTED=locally on linux and trybots
R=kwiberg@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/46749005

Cr-Commit-Position: refs/heads/master@{#8918}
15 files changed