arm64: looprestoration: Fix use of the wrong register

When renumbering argument registers in
1648c232, this one register
reference was missed.

The missed register was meant to compare h with 2, but accidentally
ended up comparing bitdepth_max to 2. In the case of 8 bpc, there's
actually no bitdepth_max parameter, so it ended up comparing an
uninitialized value.