internal/cpu: use correct variable when parsing CPU features lamcas and lam_bh on...

internal/cpu: use correct variable when parsing CPU features lamcas and lam_bh on loong64

Change-Id: I5019f4e32243911f735f775bcb3c0dba5adb4162
Reviewed-on: https://go-review.googlesource.com/c/go/+/655395
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Meidan Li <limeidan@loongson.cn>
Reviewed-by: sophie zhao <zhaoxiaolin@loongson.cn>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>