Fix references to Hafnium functions which no longer exist.

Change-Id: I149a4f51597f2e9dbf7cc290217a93d83281d17d
diff --git a/src/api.c b/src/api.c
index a514bf6..1457d58 100644
--- a/src/api.c
+++ b/src/api.c
@@ -111,7 +111,7 @@
 		break;
 	}
 
-	/* Set the return value for the primary VM's call to HF_VCPU_RUN. */
+	/* Set the return value for the primary VM's call to FFA_RUN. */
 	arch_regs_set_retval(&next->regs, primary_ret);
 
 	/* Mark the current vCPU as waiting. */