tcg/s390x: Fix tcg_out_dup_vec vs general registers

tcg/s390x: Fix tcg_out_dup_vec vs general registers

We copied the data from the general register input to the
vector register output, but have not yet replicated it.
We intended to fall through into the vector-vector case,
but failed to redirect the input register.

This is caught by an assertion failure in tcg_out_insn_VRIc,
which diagnosed the incorrect register class.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>