platforms: fix clock build for macOS (yet again)

src/lib/cdev/posix/cdev_platform.cpp

@@ -379,8 +379,8 @@ extern "C" {
 
 				// Get the current time
 				struct timespec ts;
-				// px4_sem_timedwait is implemented using CLOCK_MONOTONIC,
-				// at least for lockstep, on Qurt and on Linux.
+				// Note, we can't actually use CLOCK_MONOTONIC on macOS
+				// but that's hidden and implemented in px4_clock_gettime.
 				px4_clock_gettime(CLOCK_MONOTONIC, &ts);
 
 				// Calculate an absolute time in the future