target/riscv: Fix vslide1up.vf and vslide1down.vf

target/riscv: Fix vslide1up.vf and vslide1down.vf

vslide1up_##BITWIDTH is used by the vslide1up.vx and vslide1up.vf. So its
scalar input should be uint64_t to hold the 64 bits float register.And the
same for vslide1down_##BITWIDTH.

This bug is caught when run these instructions on qemu-riscv32.

Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
Reviewed-by: Weiwei Li <liweiwei@iscas.ac.cn>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Message-ID: <20230213094550.29621-1-zhiwei_liu@linux.alibaba.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>