Remove two unnecessary variables from evaluate_subexp_standard

Remove two unnecessary variables from evaluate_subexp_standard

I noticed a couple of spots in evaluate_subexp_standard that looked
like:

    value *result;
    result = something;
    return result;

This patch simplifies these spots to a simple "return".

gdb/ChangeLog
2020-11-25  Tom Tromey  <tom@tromey.com>

	* eval.c (evaluate_subexp_standard): Remove unnecessary
	variables.