Remove an unreachable expression.

The goto always jumps into the loop so the for's initialisation
expression can never be executed. Clang warns about this.

Change-Id: I3c3d4b8430754099e9ca6fd20101868c40165245
diff --git a/crypto/bn/generic.c b/crypto/bn/generic.c
index 0e7d867..c240a54 100644
--- a/crypto/bn/generic.c
+++ b/crypto/bn/generic.c
@@ -1068,7 +1068,7 @@
   tp[num + 1] = 0;
   goto enter;
 
-  for (i = 0; i < num; i++) {
+  for (; i < num; i++) {
     c0 = 0;
     ml = bp[i];
 #ifdef mul64