raid6: riscv: replace one load with a move to speed up the caculation

raid6: riscv: replace one load with a move to speed up the caculation

Since wp$$==wq$$, it doesn't need to load the same data twice, use move
instruction to replace one of the loads to let the program run faster.

Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
Link: https://lore.kernel.org/r/20250718072711.3865118-3-zhangchunyan@iscas.ac.cn
Signed-off-by: Paul Walmsley <pjw@kernel.org>