Minor simplification to the padding extension logic.

With the fastradio stuff gone, the padding computation is slightly more
straight-forward.

Change-Id: I67ede92fdf5f34c265c7a44e4cdc1a5ce5416df2
Reviewed-on: https://boringssl-review.googlesource.com/5482
Reviewed-by: Adam Langley <agl@google.com>
1 file changed