When --enable-coefficient-range-checking isn't specificed, clamp the
coefficient at each stage.

This doesn't change the decoder behaviour for existing AV1 streams.
However, some AV1 bitstreams that would have been rejected by the
decoder as illegal (range check failure) are now legal bitstreams.

There is no impact on video quality.

BUG=aomedia:30

Change-Id: Ifa01186bae6bfe5d7712298e33d964c20f88435e