sim: cgen-accfp: Fix pointer sign warnings

sim: cgen-accfp: Fix pointer sign warnings

When compiling we get the following warnings:

  common/cgen-accfp.c: In function 'fixsfsi':
  common/cgen-accfp.c:370:18: warning: pointer targets in passing argument 1 of 'sim_fpu_to32i' differ in signedness [-Wpointer-sign]
     sim_fpu_to32i (&res, &op1, sim_fpu_round_near);
                    ^
  common/cgen-accfp.c: In function 'fixdfsi':
  common/cgen-accfp.c:381:18: warning: pointer targets in passing argument 1 of 'sim_fpu_to32i' differ in signedness [-Wpointer-sign]
     sim_fpu_to32i (&res, &op1, sim_fpu_round_near);
                    ^