[WebAssembly] Fix copypasta.

Noticed by dschff in http://reviews.llvm.org/rL252203

llvm-svn: 252208
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInteger.td b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInteger.td
index d38be09..4b45ccb 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInteger.td
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInteger.td
@@ -52,4 +52,4 @@
                    "i32.select $dst, $cond, $lhs, $rhs">;
 def SELECT_I64 : I<(outs I64:$dst), (ins I32:$cond, I64:$lhs, I64:$rhs),
                    [(set I64:$dst, (select I32:$cond, I64:$lhs, I64:$rhs))],
-                   "i32.select $dst, $cond, $lhs, $rhs">;
+                   "i64.select $dst, $cond, $lhs, $rhs">;