gnu: linux-initrd: When booting, chdir to the new root before calling 'chroot'.

* guix/build/linux-initrd.scm (boot-system): Add 'chdir' call right
  before 'chroot'.

guix/build/linux-initrd.scm

@@ -318,6 +318,7 @@ (define MS_RDONLY 1)
     (if to-load
         (begin
           (format #t "loading '~a'...\n" to-load)
+          (chdir "/root")
           (chroot "/root")
           ;; TODO: Remove /lib, /share, and /loader.go.
           (catch #t