Fix a typo in the RSA benchmark.

Also fix error handling in RSAPublicKeyFromBuf().

BUG=1210
TEST=none

Review URL: http://codereview.chromium.org/660310
diff --git a/utils/file_keys.c b/utils/file_keys.c
index 1aac93f..98e878a 100644
--- a/utils/file_keys.c
+++ b/utils/file_keys.c
@@ -51,7 +51,7 @@
 
 RSAPublicKey* RSAPublicKeyFromFile(const char* input_file) {
   uint32_t len;
-  RSAPublicKey* key;
+  RSAPublicKey* key = NULL;
   uint8_t* buf = BufferFromFile(input_file, &len);
   if (buf)
     key = RSAPublicKeyFromBuf(buf, len);