configure: fix handling of --docdir parameter

Commit ca8c0909f0 changed qemu_docdir to be docdir, then later uses the
qemu_docdir name in the final assignment. Unfortunately, one instance of
qemu_docdir was missed: the one which comes from the --docdir parameter.
This patch restores the proper handling of the --docdir parameter.

Fixes: ca8c0909f0 ("configure: build docdir like other suffixed
directories")

Signed-off-by: Bruce Rogers <brogers@suse.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20201015190742.270629-1-brogers@suse.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -969,7 +969,7 @@ for opt do
   ;;
   --with-suffix=*) qemu_suffix="$optarg"
   ;;
-  --docdir=*) qemu_docdir="$optarg"
+  --docdir=*) docdir="$optarg"
   ;;
   --sysconfdir=*) sysconfdir="$optarg"
   ;;
@@ -5776,7 +5776,6 @@ fi
 qemu_confdir="$sysconfdir/$qemu_suffix"
 qemu_moddir="$libdir/$qemu_suffix"
 qemu_datadir="$datadir/$qemu_suffix"
-qemu_docdir="$docdir/$qemu_suffix"
 qemu_localedir="$datadir/locale"
 qemu_icondir="$datadir/icons"
 qemu_desktopdir="$datadir/applications"