[ghex] build: Fix application of docdir option if specified

[Logan Rathbone <larathbone src gnome org>]

commit f6be8a460060694ab594387a36fba2f06ca5093d
Author: Logan Rathbone <poprocks gmail com>
Date:   Tue Apr 5 14:14:25 2022 -0400

    build: Fix application of docdir option if specified

 docs/meson.build | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)
---
diff --git a/docs/meson.build b/docs/meson.build
index 2b65cd3..c0bf2b5 100644
--- a/docs/meson.build
+++ b/docs/meson.build
@@ -17,15 +17,13 @@ if get_option('werror')
   gidocgen_common_args += ['--fatal-warnings']
 endif
 
-docs_dir = join_paths(ghex_datadir, 'doc')
-
 if get_option('gtk_doc')
   gtkhex_toml = configure_file(
     input: 'GtkHex.toml.in',
     output: 'GtkHex.toml',
     configuration: toml_conf,
     install: true,
-    install_dir: join_paths(docs_dir, gir_apiname),
+    install_dir: join_paths(ghex_docdir, gir_apiname),
   )
 
   docs_cmd = [
@@ -44,6 +42,6 @@ if get_option('gtk_doc')
     command: docs_cmd,
     build_by_default: true,
     install: true,
-    install_dir: docs_dir,
+    install_dir: ghex_docdir,
   )
 endif