dawn/node: fix binding for GPUBufferMapState

This fixes a linking problem.
The conversion function should be a member of the Convert class,
not a freestanding function.

Change-Id: Ifa351e4ba6fb0e95fed311a11e9dc56e13eb1a0b
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/129260
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>
Kokoro: Kokoro <noreply+kokoro@google.com>

src/dawn/node/binding/Converter.cpp

@@ -1724,7 +1724,7 @@ bool Converter::Convert(interop::GPUQueryType& out, wgpu::QueryType in) {
     return false;
 }
 
-bool Convert(interop::GPUBufferMapState& out, wgpu::BufferMapState in) {
+bool Converter::Convert(interop::GPUBufferMapState& out, wgpu::BufferMapState in) {
     switch (in) {
         case wgpu::BufferMapState::Unmapped:
             out = interop::GPUBufferMapState::kUnmapped;