include: correct the definition of MSTATUS_VS

Accordind to the RISC-V privileged specification, the VS filed is
mstatus[10:9] instead of mstatus[24:23]. Modify the MSTATUS_VS
to the correct value.

Reported-by: I-Cheng Cheng <i-cheng.cheng@sifive.com>
Signed-off-by: Vincent Chen <vincent.chen@sifive.com>
Reviewed-by: Xiang W <wxjstz@126.com>
Reviewed-by: Anup Patel <anup@brainfault.org>