don't square error term twice

don't square error term twice

The cubic code erroneously passed the error square term to a function
which in turn squares the error term.

R=reed@google.com
BUG=skia:3877
Committed: https://skia.googlesource.com/skia/+/1bfcaa463650dc4c51cef074dd770a7158b096b7

[caryclark, 2015-06-01 15:30:54]

The CQ bit was checked by caryclark@google.com

[commit-bot: I haz the power, 2015-06-01 15:31:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1163843003/1

[commit-bot: I haz the power, 2015-06-01 15:31:13]

Note for Reviewers:
The CQ is waiting for an approval.
If you believe that the CL is not ready yet, or if you would like to L-G-T-M
with comments then please uncheck the CQ checkbox.

Waiting for LGTM from valid reviewer(s) till 2015-06-01 21:31 UTC

[reed1, 2015-06-01 15:40:28]

reed@google.com changed reviewers:
+ reed@google.com

[reed1, 2015-06-01 15:40:28]

lgtm

[commit-bot: I haz the power, 2015-06-01 15:40:52]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/1bfcaa463650dc4c51cef074dd770a7158b096b7