psci: rework cpu_off assertion and minor cleanups

This patch:

1. removes a duplicate assertion to check that the only error
   condition that can be returned while turning a cpu off is
   PSCI_E_DENIED. Having this assertion after calling
   psci_afflvl_off() is sufficient.

2. corrects some incorrect usage of 'its' vs 'it is'

3. removes some unwanted white spaces

Change-Id: Icf014e269b54f5be5ce0b9fbe6b41258e4ebf403
diff --git a/common/psci/psci_common.c b/common/psci/psci_common.c
index 8eb0213..ba0a379 100644
--- a/common/psci/psci_common.c
+++ b/common/psci/psci_common.c
@@ -196,7 +196,7 @@
 /*******************************************************************************
  * This routine does the heavy lifting for psci_change_state(). It examines the
  * state of each affinity instance at the next lower affinity level and decides
- * it's final state accordingly. If a lower affinity instance is ON then the
+ * its final state accordingly. If a lower affinity instance is ON then the
  * higher affinity instance is ON. If all the lower affinity instances are OFF
  * then the higher affinity instance is OFF. If atleast one lower affinity
  * instance is SUSPENDED then the higher affinity instance is SUSPENDED. If only
@@ -210,7 +210,7 @@
 	unsigned long tempidr;
 	aff_map_node *lo_aff_node;
 
-	/* Cannot calculate lowest affinity state. It's simply assigned */
+	/* Cannot calculate lowest affinity state. It is simply assigned */
 	assert(aff_node->level > MPIDR_AFFLVL0);
 
 	/*
@@ -248,7 +248,7 @@
 
 		/*
 		 * At least one X-1 needs to be suspended for X to be suspended
-		 * but it's effectively on for the affinity_info call.
+		 * but it is effectively on for the affinity_info call.
 		 * SUSPEND > ON_PENDING > OFF.
 		 */
 		case PSCI_STATE_SUSPEND:
@@ -424,8 +424,8 @@
 
 /*******************************************************************************
  * An affinity level could be on, on_pending, suspended or off. These are the
- * logical states it can be in. Physically either it's off or on. When it's in
- * the state on_pending then it's about to be turned on. It's not possible to
+ * logical states it can be in. Physically either it is off or on. When it is in
+ * the state on_pending then it is about to be turned on. It is not possible to
  * tell whether that's actually happenned or not. So we err on the side of
  * caution & treat the affinity level as being turned off.
  ******************************************************************************/