ART: mterp arm/arm64 cleanup

Assembly code cleanup in response to comments from already-submitted
CL: https://android-review.googlesource.com/#/c/188977/

Change-Id: I0ea85c5759a08cb50ef3e97dc5cf79b3ba041640
diff --git a/runtime/interpreter/mterp/arm/funop.S b/runtime/interpreter/mterp/arm/funop.S
index d7a0859..1b8bb8b 100644
--- a/runtime/interpreter/mterp/arm/funop.S
+++ b/runtime/interpreter/mterp/arm/funop.S
@@ -6,11 +6,10 @@
      */
     /* unop vA, vB */
     mov     r3, rINST, lsr #12          @ r3<- B
-    mov     r9, rINST, lsr #8           @ r9<- A+
     VREG_INDEX_TO_ADDR r3, r3           @ r3<- &vB
     flds    s0, [r3]                    @ s0<- vB
+    ubfx    r9, rINST, #8, #4           @ r9<- A
     FETCH_ADVANCE_INST 1                @ advance rPC, load rINST
-    and     r9, r9, #15                 @ r9<- A
     $instr                              @ s1<- op
     GET_INST_OPCODE ip                  @ extract opcode from rINST
     VREG_INDEX_TO_ADDR r9, r9           @ r9<- &vA