Use the FloatRelation enum to hold the comparison result (missed
in commit 71bfd65c

 "softfloat: Name compare relation enum").

Inspired-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>