ch: Include unistd.h in ch_events.c

There's a call to read() in the file but corresponding include of
unistd.h is missing causing a build failure.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>

src/ch/ch_events.c

@@ -20,6 +20,8 @@
 
 #include <config.h>
 
+#include <unistd.h>
+
 #include "ch_domain.h"
 #include "ch_events.h"
 #include "ch_process.h"