Fix MISRA rule 8.4 Part 1

Rule 8.4: A compatible declaration shall be visible when
          an object or function with external linkage is defined

Fixed for:
	make DEBUG=1 PLAT=fvp LOG_LEVEL=50 all

Change-Id: I7c2ad3f5c015411c202605851240d5347e4cc8c7
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>
diff --git a/drivers/arm/tzc/tzc400.c b/drivers/arm/tzc/tzc400.c
index 34462a9..0999fa5 100644
--- a/drivers/arm/tzc/tzc400.c
+++ b/drivers/arm/tzc/tzc400.c
@@ -34,7 +34,7 @@
 	uint8_t num_regions;
 } tzc400_instance_t;
 
-tzc400_instance_t tzc400;
+static tzc400_instance_t tzc400;
 
 static inline unsigned int _tzc400_read_build_config(uintptr_t base)
 {