Fix C function signature with no parameters

Use void in parameter types to satisfy the compiler.

Change-Id: I6a6a696449f043209b9f32290b914bbae54aefb7
Signed-off-by: Khang D Nguyen <khangng@os.amperecomputing.com>
diff --git a/log.c b/log.c
index 16f671f..93a6f5c 100644
--- a/log.c
+++ b/log.c
@@ -40,7 +40,7 @@
 	va_end(ap);
 }
 
-void cper_set_log_stdio()
+void cper_set_log_stdio(void)
 {
 	log_type = CPER_LOG_STDIO;
 }