Resolve signed-unsigned comparison issues

A recent commit 030567e6f51731982a7e71cbd387de93bc0e35fd added U()/ULL()
macro to TF constants. This has caused some signed-unsigned comparison
warnings / errors in the TF static analysis.

This patch addresses these issues by migrating impacted variables from
signed ints to unsigned ints and vice verse where applicable.

Change-Id: I4b4c739a3fa64aaf13b69ad1702c66ec79247e53
Signed-off-by: David Cunado <david.cunado@arm.com>
diff --git a/lib/cpus/errata_report.c b/lib/cpus/errata_report.c
index 1e1fc78..8d9f704 100644
--- a/lib/cpus/errata_report.c
+++ b/lib/cpus/errata_report.c
@@ -72,7 +72,7 @@
 	const char *msg __unused;
 
 
-	assert(status >= 0 && status < ARRAY_SIZE(errata_status_str));
+	assert(status < ARRAY_SIZE(errata_status_str));
 	assert(cpu);
 	assert(id);