target/i386: decode-new: avoid out-of-bounds access to xmm_regs[-1]

target/i386: decode-new: avoid out-of-bounds access to xmm_regs[-1]

If the destination is a memory register, op->n is -1.  Going through
tcg_gen_gvec_dup_imm path is both useless (the value has been stored
by the gen_* function already) and wrong because of the out-of-bounds
access.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>