Revert "vp9_loopfilter.c: zero lfl_uv"

Revert "vp9_loopfilter.c: zero lfl_uv"

This reverts commit 13d0955b250bcb7eac99034e7b1677d3d026b569.

Reason for revert:
this should be investigated further to ensure the memset is really
necessary outside of the static analysis pass.

Original change's description:
> vp9_loopfilter.c: zero lfl_uv
>
> The initialization depends on cm and mi_row which static
> analysis does not approve of.
>
> Clears a static analysis warning:
> warning: The right operand of '+' is a garbage value
> const loop_filter_thresh *lfi = lfthr + *lfl;
>
> Change-Id: I8c863ced2b1e9a7e10103b7281098f20941a6ca2

TBR=johannkoenig@google.com,marpan@google.com,builds@webmproject.org,jianj@google.com

Change-Id: Icadb6438fbcddba747622f06f2eadebdb333edf6
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