AP_Compass: HMC5843: remove useless delay

There's no need to add a delay after suspending timer in the
initialization. Also initialize _bus_sem earlier, like is done in
AK8963.

libraries/AP_Compass/AP_Compass_HMC5843.cpp

@@ -244,10 +244,9 @@ AP_Compass_HMC5843::init()
     uint16_t expected_yz = 715;
     float gain_multiple = 1.0;
 
+    _bus_sem = _bus->get_semaphore();
     hal.scheduler->suspend_timer_procs();
-    hal.scheduler->delay(10);
 
-    _bus_sem = _bus->get_semaphore();
     if (!_bus_sem->take(HAL_SEMAPHORE_BLOCK_FOREVER)) {
         hal.scheduler->panic(PSTR("Failed to get HMC5843 semaphore"));
     }