Bug fix: Missing variable name in conv2d

A step comparing data types didn't specify where one of the types
was coming from. Oops!

index.bs

@@ -2302,7 +2302,7 @@ partial interface MLGraphBuilder {
     1. Let |filterSize| be the [=list/size=] of |filter|.{{MLOperand/[[descriptor]]}}.{{MLOperandDescriptor/dimensions}}.
     1. If |inputSize| is not 4, then [=exception/throw=] a "{{DataError}}" {{DOMException}}.
     1. If |filterSize| is not 4, then [=exception/throw=] a "{{DataError}}" {{DOMException}}.
-    1. If |input|.{{MLOperand/[[descriptor]]}}.{{MLOperandDescriptor/dataType}} is not the same as {{MLOperand/[[descriptor]]}}.{{MLOperandDescriptor/dataType}}, then [=exception/throw=] a {{TypeError}}.
+    1. If |input|.{{MLOperand/[[descriptor]]}}.{{MLOperandDescriptor/dataType}} is not the same as |filter|.{{MLOperand/[[descriptor]]}}.{{MLOperandDescriptor/dataType}}, then [=exception/throw=] a {{TypeError}}.
     1. If |options|.{{MLConvTranspose2dOptions/padding}} does not [=map/exist=], set it to the [=/list=] « 0, 0, 0, 0 ».
     1. Else if the [=list/size=] of |options|.{{MLConvTranspose2dOptions/padding}} is not 4, then [=exception/throw=] a "{{DataError}}" {{DOMException}}.
     1. If |options|.{{MLConvTranspose2dOptions/strides}} does not [=map/exist=], set it to the [=/list=] « 1, 1 ».