metropolis/pkg/kexec: fix scanner error check

Change-Id: Ib2fff5e782ebd0fcef334b509900af995ce92264
Reviewed-on: https://review.monogon.dev/c/monogon/+/2965
Tested-by: Jenkins CI
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/metropolis/pkg/kexec/kexec.go b/metropolis/pkg/kexec/kexec.go
index 4d05037..7109903 100644
--- a/metropolis/pkg/kexec/kexec.go
+++ b/metropolis/pkg/kexec/kexec.go
@@ -36,8 +36,8 @@
 				// We have no RSDP, no need to pass it
 				break
 			}
-			if err != nil {
-				return fmt.Errorf("failed to read EFI systab: %w", err)
+			if s.Err() != nil {
+				return fmt.Errorf("failed to read EFI systab: %w", s.Err())
 			}
 			parts := strings.SplitN(s.Text(), "=", 2)
 			// There are two ACPI RDSP revisions, 1.0 and 2.0.