alpha: Use mb for rmb
alpha: Use mb for rmb

Alpha never have a rmb instruction.
Just use mb for rmb.

Signed-off-by: Jiaxun Yang <accc0069bb3ff62ae1a181f9cf05aee7ddbd8eff@flygoat.com>

xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS,xianyi/OpenBLAS