arm/aarch64: vp9: Fix vertical alignment

Align the second/third operands as they usually are.

Due to the wildly varying sizes of the written out operands
in aarch64 assembly, the column alignment is usually not as clear
as in arm assembly.

This is cherrypicked from libav commit
7995ebfa.
Signed-off-by: Martin Storsjö <martin@martin.st>