input: Don't leak the initial keymap

weston_xkb_info_create() takes ownership of the xkb_keymap instance so
we should drop our reference or we would leak it later if the keymap
was changed.
diff --git a/src/input.c b/src/input.c
index 07e9d6c..902cfb8 100644
--- a/src/input.c
+++ b/src/input.c
@@ -1954,6 +1954,7 @@
 	}
 
 	ec->xkb_info = weston_xkb_info_create(keymap);
+	xkb_keymap_unref(keymap);
 	if (ec->xkb_info == NULL)
 		return -1;