Use the NLIMBS macro rather than try and calculate the number of limbs

Reviewed-by: NBernd Edlinger <bernd.edlinger@hotmail.de>
(Merged from https://github.com/openssl/openssl/pull/5105)

crypto/ec/curve448/arch_32/f_impl.h

@@ -20,7 +20,7 @@ void gf_add_RAW(gf out, const gf a, const gf b)
 {
     unsigned int i;
 
-    for (i = 0; i < sizeof(*out) / sizeof(out->limb[0]); i++) {
+    for (i = 0; i < NLIMBS; i++) {
         out->limb[i] = a->limb[i] + b->limb[i];
     }
 }