cmd/compile: ignore SliceExpr.CheckPtrCall for mknode
cmd/compile: ignore SliceExpr.CheckPtrCall for mknode

CL 343972 added SliceExpr.CheckPtrCall field but forgot to add ignore
tag for mknode. This CL adds the missing tag.

Change-Id: Ib39bff3d456063bdc10fc17b4047b8392d373bf1
Reviewed-on: https://go-review.googlesource.com/c/go/+/345431
Trust: Cuong Manh Le <54b4457f1dff6823379654eb5867596497ba782f@gmail.com>
Run-TryBot: Cuong Manh Le <54b4457f1dff6823379654eb5867596497ba782f@gmail.com>
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

CAFxX/go,golang/go,golang/go,CAFxX/go,nawawi/go,golang/go,CAFxX/go,CAFxX/go,cloudflare/go,nawawi/go,CAFxX/go,golang/go,nawawi/go,CAFxX/go,CAFxX/go,CAFxX/go,cloudflare/go,cloudflare/go,nawawi/go,nawawi/go,golang/go,golang/go,cloudflare/go,golang/go,cloudflare/go,nawawi/go,cloudflare/go,cloudflare/go,cloudflare/go,golang/go,nawawi/go,nawawi/go