Fix upper bound of loopfilter hev strength.

Fixes #21.
3 jobs for master in 1 minute and 7 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed build-debian #823
debian amd64

00:00:21

passed build-win32 #824
win32

00:00:21

passed build-win64 #825
win64

00:00:24