docs: Fix dot_rst_html_in definition

As the name clearly implies, it's supposed to list the .html.in
files that are generated from .rst files, but it mistakenly lists
the corresponding .html files instead.
Signed-off-by: NAndrea Bolognani <abologna@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

docs/Makefile.am

@@ -325,7 +325,7 @@ dot_html_in = \
 dot_rst = \
   $(notdir $(wildcard $(srcdir)/*.rst))
 dot_rst_html_in = \
-  $(dot_rst:%.rst=%.html)
+  $(dot_rst:%.rst=%.html.in)
 dot_html = \
   $(dot_html_generated_in:%.html.in=%.html) \
   $(dot_html_in:%.html.in=%.html) \