cleanup: rename armv4_5 to arm for readability

Nothing more than a name change, just to make reading
the code a bit simpler.

Change-Id: I73a16b7302b48ce07d9688162955aae71d11eb45
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/390
Tested-by: jenkins
Reviewed-by: Øyvind Harboe <oyvindharboe@gmail.com>

src/target/cortex_a.h

@@ -85,7 +85,7 @@ static inline struct cortex_a8_common *
 target_to_cortex_a8(struct target *target)
 {
 	return container_of(target->arch_info, struct cortex_a8_common,
-			armv7a_common.armv4_5_common);
+			armv7a_common.arm);
 }
 
 #endif /* CORTEX_A8_H */