Remove undef

Author: dianqk

llvm/test/CodeGen/AArch64/machine-cp-sub-reg.mir

@@ -10,7 +10,7 @@ body:             |
   ; CHECK-NEXT:   successors: %bb.1(0x80000000)
   ; CHECK-NEXT:   liveins: $w0
   ; CHECK-NEXT: {{  $}}
-  ; CHECK-NEXT:   $x8 = ORRXrs $xzr, undef $x0, 0, implicit $w0
+  ; CHECK-NEXT:   $x8 = ORRXrs $xzr, $x0, 0, implicit $w0
   ; CHECK-NEXT:   $w8 = ORRWrs $wzr, $w0, 0, implicit-def $x8
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT: bb.1:
@@ -22,7 +22,7 @@ body:             |
     successors: %bb.1(0x80000000)
     liveins: $w0
 
-    $x8 = ORRXrs $xzr, undef $x0, 0, implicit $w0
+    $x8 = ORRXrs $xzr, $x0, 0, implicit $w0
     $w8 = ORRWrs $wzr, $w0, 0, implicit-def $x8
 
   bb.1: