Can't boot into new configuration after nix-rebuild, raspberry pi3 B

I changed the config.fileSystems directly in nixpkgs/nixos/modules/installer/cd-dvd/sd-image.nix in the local copy I have of nixpkgs and that didn’t work… for understandable reasons.

This is what I changed:

diff --git a/nixos/modules/installer/cd-dvd/sd-image.nix b/nixos/modules/installer/cd-dvd/sd-image.nix
index 901c60be..80b6e715 100644
--- a/nixos/modules/installer/cd-dvd/sd-image.nix
+++ b/nixos/modules/installer/cd-dvd/sd-image.nix
@@ -113,13 +113,13 @@ in

   config = {
     fileSystems = {
-      "/boot/firmware" = {
+      "/boot" = {
         device = "/dev/disk/by-label/FIRMWARE";
         fsType = "vfat";
         # Alternatively, this could be removed from the configuration.
         # The filesystem is not needed at runtime, it could be treated
         # as an opaque blob instead of a discrete FAT32 filesystem.
-        options = [ "nofail" "noauto" ];
+        #options = [ "nofail" "noauto" ];
       };
       "/" = {
         device = "/dev/disk/by-label/NIXOS_SD";

The error I get: