target/arm: Fix LD1W and LDFF1W (scalar plus vector)

target/arm: Fix LD1W and LDFF1W (scalar plus vector)

'I' was being double-incremented; correctly within the inner loop
and incorrectly within the outer loop.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Laurent Desnogues <laurent.desnogues@gmail.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Message-id: 20180711103957.3040-1-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>