go-steamworks: fix SteamUserStats.GetAchievement on Windows (hajimeho…

…shi#5)

This one is a sneaky one, since it's Windows-specific
and it was impossible to debug on Linux why some players report
all of their achievements being unlocked.

Turns out, it's a Windows-specific typo in the library.

steamworks_windows.go

@@ -288,7 +288,7 @@ func (s steamUserStats) GetAchievement(name string) (achieved, success bool) {
 	cname := append([]byte(name), 0)
 	defer runtime.KeepAlive(cname)
 
-	v, err := theDLL.call(flatAPI_ISteamUserStats_SetAchievement, uintptr(s), uintptr(unsafe.Pointer(&cname[0])), uintptr(unsafe.Pointer(&achieved)))
+	v, err := theDLL.call(flatAPI_ISteamUserStats_GetAchievement, uintptr(s), uintptr(unsafe.Pointer(&cname[0])), uintptr(unsafe.Pointer(&achieved)))
 	if err != nil {
 		panic(err)
 	}