linux_rpi: ignoreConfigErrors

Since 37789d9eaa566f5d0bdeaaecd9cb3b0991dab6e9 the ignoreConfigErrors is
no longer enabled on aarch64, which fails the rpi kernel build

Change-Id: I1f9e21badf53fbfdcd3da561f7c398a353c4e9a9

pkgs/os-specific/linux/kernel/linux-rpi.nix

···
             platforms = with lib.platforms; arm ++ aarch64;
             hydraPlatforms = [ "aarch64-linux" ];
           };
+      ignoreConfigErrors = true;
     }
     // (args.argsOverride or { })
   ))