Ensure void in empty parameter list

According to ISO/IEC 9899:2011, section 6.7.6.3, "Function declarators
(including prototypes)": "The special case of an unnamed parameter of
type void as the only item in the list specifies that the function has
no parameters."
Signed-off-by: Guilherme Maciel Ferreira <guilherme.maciel.ferreira@gmail.com>

src/samples/pahopub.c

@@ -55,7 +55,7 @@
 volatile int toStop = 0;
 
 
-void usage()
+void usage(void)
 {
 	printf("MQTT stdin publisher\n");
 	printf("Usage: stdinpub topicname <options>, where options are:\n");

src/samples/stdinpub.c

@@ -76,7 +76,7 @@ struct
 };
 
 
-void usage()
+void usage(void)
 {
 	printf("MQTT stdin publisher\n");
 	printf("Usage: stdinpub topicname <options>, where options are:\n");

src/samples/stdinpuba.c

@@ -75,7 +75,7 @@ struct
 };
 
 
-void usage()
+void usage(void)
 {
 	printf("MQTT stdin publisher\n");
 	printf("Usage: stdinpub topicname <options>, where options are:\n");

src/samples/stdoutsub.c

@@ -76,7 +76,7 @@ struct opts_struct
 };
 
 
-void usage()
+void usage(void)
 {
 	printf("MQTT stdout subscriber\n");
 	printf("Usage: stdoutsub topicname <options>, where options are:\n");

src/samples/stdoutsuba.c

@@ -88,7 +88,7 @@ struct
 };
 
 
-void usage()
+void usage(void)
 {
 	printf("MQTT stdout subscriber\n");
 	printf("Usage: stdoutsub topicname <options>, where options are:\n");