In do_ldst(), the calculation of the offset needs to be based on the
size of the memory access, not the size of the elements in the
vector.  This meant we were getting it wrong for the widening and
narrowing variants of the various VLDR and VSTR insns.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210628135835.6690-2-peter.maydell@linaro.org