hevcdsp: remove an unneeded variable in the loop filter
beta0 and beta1 will always be the same within a CU

Signed-off-by: Mickaël Raulet <mraulet@insa-rennes.fr>

cherry picked from commit 4a23d824741a289c7d2d2f2871d1e2621b63fa1b
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
