Really fix instruction decoding for throw verification error.

The decoder was not populating register vA and vB correctly and the fix
didn't fix it correctly either. This time it's correct.

Change-Id: If97b367f6b1dff5fbbb30c0ad9f767e2b1d08326
diff --git a/src/dex_instruction.cc b/src/dex_instruction.cc
index d768c0b..e0b10f9 100644
--- a/src/dex_instruction.cc
+++ b/src/dex_instruction.cc
@@ -91,13 +91,10 @@
     case k10t:       // op +AA
       vA = (int8_t) INST_AA(insn);              // sign-extend 8-bit value
       break;
-    case k20bc:      // op AA, kind@BBBB
-      vA = INST_A(insn);
-      vB = INST_B(insn);
-      break;
     case k20t:       // op +AAAA
       vA = (int16_t) FETCH(1);                   // sign-extend 16-bit value
       break;
+    case k20bc:      // op AA, kind@BBBB
     case k21c:       // op vAA, thing@BBBB
     case k22x:       // op vAA, vBBBB
       vA = INST_AA(insn);