doc: efi-stub.txt: Fix arm64 paths

Update documented paths for arm64 files to match current tree.
Signed-off-by: Alan Ott <alan@softiron.co.uk>
Cc: Roy Franz <roy.franz@linaro.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>

Documentation/efi-stub.txt

@@ -10,12 +10,12 @@ arch/x86/boot/header.S and arch/x86/boot/compressed/eboot.c,
 respectively. For ARM the EFI stub is implemented in
 arch/arm/boot/compressed/efi-header.S and
 arch/arm/boot/compressed/efi-stub.c. EFI stub code that is shared
-between architectures is in drivers/firmware/efi/efi-stub-helper.c.
+between architectures is in drivers/firmware/efi/libstub.
 
 For arm64, there is no compressed kernel support, so the Image itself
 masquerades as a PE/COFF image and the EFI stub is linked into the
 kernel. The arm64 EFI stub lives in arch/arm64/kernel/efi-entry.S
-and arch/arm64/kernel/efi-stub.c.
+and drivers/firmware/efi/libstub/arm64-stub.c.
 
 By using the EFI boot stub it's possible to boot a Linux kernel
 without the use of a conventional EFI boot loader, such as grub or