initialise |n| parameter in bn_test.cc to avoid compiler warning.

crypto/bn/bn_test.cc:404:44: error: ‘n’ may be used uninitialized in this
function [-Werror=maybe-uninitialized]

Change-Id: Id590dfee4b9ae1a4fbd0965e133310dac0d06ed3

crypto/bn/bn_test.cc

@@ -392,7 +392,7 @@ static bool TestLShift1(FileTest *t, BN_CTX *ctx) {
 static bool TestLShift(FileTest *t, BN_CTX *ctx) {
   ScopedBIGNUM a = GetBIGNUM(t, "A");
   ScopedBIGNUM lshift = GetBIGNUM(t, "LShift");
-  int n;
+  int n = 0;
   if (!a || !lshift || !GetInt(t, &n, "N")) {
     return false;
   }
@@ -412,7 +412,7 @@ static bool TestLShift(FileTest *t, BN_CTX *ctx) {
 static bool TestRShift(FileTest *t, BN_CTX *ctx) {
   ScopedBIGNUM a = GetBIGNUM(t, "A");
   ScopedBIGNUM rshift = GetBIGNUM(t, "RShift");
-  int n;
+  int n = 0;
   if (!a || !rshift || !GetInt(t, &n, "N")) {
     return false;
   }