build-system/haskell: Adjust to new 'modify-phases' syntax.

* guix/build/haskell-build-system.scm (%standard-phases): Add missing
  quotes, as needed since commit f8503e2b.

guix/build/haskell-build-system.scm

@@ -196,13 +196,13 @@ (define* (haddock #:key outputs haddock? haddock-flags #:allow-other-keys)
 
 (define %standard-phases
   (modify-phases gnu:%standard-phases
-    (add-before configure setup-compiler setup-compiler)
-    (add-before install haddock haddock)
-    (add-after install register register)
-    (replace install install)
-    (replace check check)
-    (replace build build)
-    (replace configure configure)))
+    (add-before 'configure 'setup-compiler setup-compiler)
+    (add-before 'install 'haddock haddock)
+    (add-after 'install 'register register)
+    (replace 'install install)
+    (replace 'check check)
+    (replace 'build build)
+    (replace 'configure configure)))
 
 (define* (haskell-build #:key inputs (phases %standard-phases)
                         #:allow-other-keys #:rest args)