Fix warnings: variable 'kret' set but not use

[27/47] Compiling C object pcscd.p/src_hotplug_macosx.c.o
../src/hotplug_macosx.c:100:16: warning: variable 'kret' set but not used [-Wunused-but-set-variable]
  100 |         kern_return_t kret;
      |                       ^
../src/hotplug_macosx.c:117:16: warning: variable 'kret' set but not used [-Wunused-but-set-variable]
  117 |         kern_return_t kret;
      |                       ^
2 warnings generated.

src/hotplug_macosx.c

@@ -97,13 +97,12 @@ static HPDriver *Drivers = NULL;
  */
 static void HPDeviceAppeared(void *refCon, io_iterator_t iterator)
 {
- kern_return_t kret;
  io_service_t obj;
 
  (void)refCon;
 
  while ((obj = IOIteratorNext(iterator)))
- kret = IOObjectRelease(obj);
+ IOObjectRelease(obj);
 
  HPScan();
 }
@@ -114,13 +113,12 @@ static void HPDeviceAppeared(void *refCon, io_iterator_t iterator)
  */
 static void HPDeviceDisappeared(void *refCon, io_iterator_t iterator)
 {
- kern_return_t kret;
  io_service_t obj;
 
  (void)refCon;
 
  while ((obj = IOIteratorNext(iterator)))
- kret = IOObjectRelease(obj);
+ IOObjectRelease(obj);
 
  HPScan();
 }