Fixed compiler warning

lib/spdylay_npn.c

@@ -36,12 +36,12 @@ int spdylay_select_next_protocol(unsigned char **out, unsigned char *outlen,
   *outlen = 6;
   for(; i < inlen; i += in[i]+1) {
     if(in[i] == 6 && memcmp(&in[i+1], "spdy/2", in[i]) == 0) {
-      *out = &in[i+1];
+      *out = (unsigned char*)&in[i+1];
       *outlen = in[i];
       return 1;
     } else if(in[i] == 8 && memcmp(&in[i+1], "http/1.1", in[i]) == 0) {
       http_selected = 1;
-      *out = &in[i+1];
+      *out = (unsigned char*)&in[i+1];
       *outlen = in[i];
       /* Go through to the next iteration, because "spdy/2" may be
          there */