Warning fixes.

apps/drivers/hmc5883/hmc5883.cpp

@@ -1045,6 +1045,7 @@ int HMC5883::check_calibration()
 		_calibrated = false;
 		// XXX Notify system via uORB
 	}
+	return 0;
 }
 
 int HMC5883::set_excitement(unsigned enable)

apps/px4/tests/test_hrt.c

@@ -39,6 +39,7 @@
 #include <nuttx/config.h>
 
 #include <sys/types.h>
+#include <sys/time.h>
 
 #include <stdio.h>
 #include <stdlib.h>

apps/px4/tests/test_uart_send.c

@@ -112,7 +112,7 @@ int test_uart_send(int argc, char *argv[])
 
 	char sample_test_uart[25];// = {'S', 'A', 'M', 'P', 'L', 'E', ' ', '\n'};
 
-	int i, r, n;
+	int i, n;
 
 	uint64_t start_time = hrt_absolute_time();