gnu: plymouth: Use gexps.

* gnu/packages/freedesktop.scm (plymouth)[arguments]: Use gexps.

gnu/packages/freedesktop.scm

@@ -2232,8 +2232,9 @@ Its features include:
          "11nfgw8yzmdbnbmyd1zfvhj4qh19w1nw0nraai08628x6mzjbbpc"))))
     (build-system gnu-build-system)
     (arguments
-     `(#:configure-flags
-       (list (string-append "--with-logo="
+     (list
+      #:configure-flags
+      '(list (string-append "--with-logo="
                             "/etc/plymouth/logo.png")
              (string-append "--with-background-color="
                             "0x00ff00")
@@ -2251,21 +2252,21 @@ Its features include:
              ;; size from ~800 MiB to a little more than 200 MiB
              "--disable-gtk")
       #:phases
-       (modify-phases %standard-phases
+      #~(modify-phases %standard-phases
           (add-after 'unpack 'make-reproducible
             (lambda _
               (substitute* "src/main.c"
                 (("__DATE__") "\"guix\""))))
           (add-before 'configure 'fix-docbook
-           (lambda* (#:key inputs #:allow-other-keys)
+            (lambda _
               (substitute* "docs/Makefile.in"
                 (("http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl")
-                (string-append (assoc-ref inputs "docbook-xsl")
+                 (string-append #$(this-package-native-input "docbook-xsl")
                                 "/xml/xsl/docbook-xsl-"
-                               ,(package-version docbook-xsl)
+                                #$(package-version (this-package-native-input "docbook-xsl"))
                                 "/manpages/docbook.xsl")))
               (setenv "XML_CATALOG_FILES"
-                     (string-append (assoc-ref inputs "docbook-xml")
+                      (string-append #$(this-package-native-input "docbook-xml")
                                      "/xml/dtd/docbook/catalog.xml")))))))
     (inputs
      (list glib pango libdrm libpng eudev))