fix sem error for linux

src/drivers/device/vdev_posix.cpp

@@ -301,6 +301,9 @@ extern "C" {
 				// Execute a blocking wait for that time in the future
 				errno = 0;
 				ret = px4_sem_timedwait(&sem, &ts);
+#ifndef __PX4_DARWIN
+				ret = errno;
+#endif
 
 				// Ensure ret is negative on failure
 				if (ret > 0) {