doc: make some Sphinx config path absolute

Make all paths absolute.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
diff --git a/doc/conf.py b/doc/conf.py
index fa7b6d2..dc80dc9 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -122,15 +122,15 @@
     "prev_next_buttons_location": None
 }
 html_title = "Zephyr Project Documentation"
-html_logo = "_static/images/logo.svg"
-html_favicon = "images/zp_favicon.png"
+html_logo = str(ZEPHYR_BASE / "doc" / "_static" / "images" / "logo.svg")
+html_favicon = str(ZEPHYR_BASE / "doc" / "images" / "zp_favicon.png")
 html_static_path = [str(ZEPHYR_BASE / "doc" / "_static")]
 html_last_updated_fmt = "%b %d, %Y"
 html_domain_indices = False
 html_split_index = True
 html_show_sourcelink = False
 html_show_sphinx = False
-html_search_scorer = "_static/js/scorer.js"
+html_search_scorer = str(ZEPHYR_BASE / "doc" / "_static" / "js" / "scorer.js")
 
 is_release = tags.has("release")  # pylint: disable=undefined-variable
 docs_title = "Docs / {}".format(version if is_release else "Latest")