Use 0 as default mach port

disk/iostat_darwin.c

@@ -26,7 +26,7 @@ gopsutil_v3_readdrivestat(DriveStats a[], int n)
 
 	match = IOServiceMatching("IOMedia");
 	CFDictionaryAddValue(match, CFSTR(kIOMediaWholeKey), kCFBooleanTrue);
-	status = IOServiceGetMatchingServices((mach_port_t) NULL, match, &drives);
+	status = IOServiceGetMatchingServices(0, match, &drives);
 	if(status != KERN_SUCCESS)
 		return -1;
 

host/smc_darwin.c

@@ -72,8 +72,7 @@ kern_return_t gopsutil_v3_open_smc(void) {
   kern_return_t result;
   io_service_t service;
 
-  service = IOServiceGetMatchingService((mach_port_t) NULL,
-                                        IOServiceMatching(IOSERVICE_SMC));
+  service = IOServiceGetMatchingService(0, IOServiceMatching(IOSERVICE_SMC));
   if (service == 0) {
     // Note: IOServiceMatching documents 0 on failure
     printf("ERROR: %s NOT FOUND\n", IOSERVICE_SMC);