target: armv7a: remove unused level_num field from armv7a_cachesize

This was never used and produces warnings on some systems.

Change-Id: I48d2c5b79890bb2d70c5fae95278b8eb62743398
Reported-by: Tommy Murphy <tm1234@users.sf.net>
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/3891
Tested-by: jenkins

src/target/armv7a.h

@@ -48,7 +48,6 @@ struct armv7a_l2x_cache {
 };
 
 struct armv7a_cachesize {
-	uint32_t level_num;
 	/*  cache dimensionning */
 	uint32_t linelen;
 	uint32_t associativity;