Use NLIMBS where appropriate to simplify the code

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

@@ -29,7 +29,7 @@ void gf_sub_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];
     }
 }
@@ -39,7 +39,7 @@ void gf_bias(gf a, int amt)
     unsigned int i;
     uint32_t co1 = ((1 << 28) - 1) * amt, co2 = co1 - amt;
 
-    for (i = 0; i < sizeof(*a) / sizeof(a->limb[0]); i++)
+    for (i = 0; i < NLIMBS; i++)
         a->limb[i] += (i == sizeof(*a) / sizeof(a->limb[0]) / 2) ? co2 : co1;
 }