tcg/optimize: Add an extra cast to fold_extract2

There is no bug, but silence a warning about computation
in int32_t being assigned to a uint64_t.

Reported-by: Coverity CID 1465220
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
1 file changed