Fix build on FreeBSD.

The freq_sysctl varaible is being redefined with a different type.

Update the first definition directly.

src/freebsd.cc

@@ -544,15 +544,13 @@ void get_acpi_fan(char *p_client_buffer, size_t client_buffer_size) {
 char get_freq(char *p_client_buffer, size_t client_buffer_size,
               const char *p_format, int divisor, unsigned int cpu) {
   int freq;
-  char *freq_sysctl;
+  char freq_sysctl[16] = {0};
 
   if (!p_client_buffer || client_buffer_size <= 0 || !p_format ||
       divisor <= 0) {
     return 0;
   }
 
-  char freq_sysctl[16] = {0};
-
   snprintf(freq_sysctl, sizeof(freq_sysctl), "dev.cpu.%d.freq", (cpu - 1));
 
   if (GETSYSCTL(freq_sysctl, freq) == 0) {