target/sparc: Change DisasCompare.c2 to int

We don't require c2 to be variable, so emphasize that.
We don't currently require c2 to be non-zero, but that will change.

Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Acked-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>