Say kNumDalvikInstructions when appropriate.

In particular, use it instead of just saying 256, and similarly for
255. The number of opcodes will be changing soon.

Change-Id: Icc77120c2673968dddd6b4003f717245d46e4159
diff --git a/vm/compiler/codegen/arm/CodegenCommon.c b/vm/compiler/codegen/arm/CodegenCommon.c
index ee5d9f5..d14dd06 100644
--- a/vm/compiler/codegen/arm/CodegenCommon.c
+++ b/vm/compiler/codegen/arm/CodegenCommon.c
@@ -30,7 +30,7 @@
 static intptr_t templateEntryOffsets[TEMPLATE_LAST_MARK];
 
 /* Track exercised opcodes */
-static int opcodeCoverage[256];
+static int opcodeCoverage[kNumDalvikInstructions];
 
 static void setMemRefType(ArmLIR *lir, bool isLoad, int memType)
 {