Fix build with -Wwrite-strings.

Change-Id: If76154c8d255600e925a408acdc674fc7dad0359
Signed-off-by: Piotr Sikora <piotrsikora@google.com>
Reviewed-on: https://boringssl-review.googlesource.com/7526
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/crypto/evp/print.c b/crypto/evp/print.c
index 6c01a92..b637c70 100644
--- a/crypto/evp/print.c
+++ b/crypto/evp/print.c
@@ -136,8 +136,7 @@
 
 static int do_rsa_print(BIO *out, const RSA *rsa, int off,
                         int include_private) {
-  char *str;
-  const char *s;
+  const char *s, *str;
   uint8_t *m = NULL;
   int ret = 0, mod_len = 0;
   size_t buf_len = 0;