Fix violations to the coding style

All coding style violations have been fixed in a previous patch and
since then, each individual patch has been checked in this regard.
However, the latest version of the checkpatch.pl script from the Linux
kernel is more advanced and it is able to flag new errors in the
Trusted Firmware codebase. This patch fixes them.

Change-Id: I1f332f2440984be85d36b231bb83260368987077
diff --git a/services/std_svc/psci/psci_common.c b/services/std_svc/psci/psci_common.c
index 7ab607d..237cf1e 100644
--- a/services/std_svc/psci/psci_common.c
+++ b/services/std_svc/psci/psci_common.c
@@ -133,7 +133,7 @@
  * been physically powered up. It is expected to be called immediately after
  * reset from assembler code.
  ******************************************************************************/
-int get_power_on_target_afflvl()
+int get_power_on_target_afflvl(void)
 {
 	int afflvl;