cmd/oci-runtime-tool: fix govet warning

Found by golangci-lint v1.60.1:

cmd/oci-runtime-tool/main.go:59:17: printf: non-constant format string in call to github.com/sirupsen/logrus.Fatalf (govet)
		logrus.Fatalf(err.Error())
		              ^

cmd/oci-runtime-tool/main.go

@@ -56,7 +56,7 @@ func before(context *cli.Context) error {
 	logLevelString := context.GlobalString("log-level")
 	logLevel, err := logrus.ParseLevel(logLevelString)
 	if err != nil {
-		logrus.Fatalf(err.Error())
+		logrus.Fatal(err)
 	}
 	logrus.SetLevel(logLevel)