[librsvg] drawing_ctx: clip() does not need a mutable reference

[Federico Mena Quintero <federico src gnome org>]

commit 0b959a95335ed5decba53803a6f822eb9a44b563
Author: Paolo Borelli <pborelli gnome org>
Date:   Sun Dec 30 18:20:48 2018 +0100

    drawing_ctx: clip() does not need a mutable reference

 rsvg_internals/src/drawing_ctx.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/rsvg_internals/src/drawing_ctx.rs b/rsvg_internals/src/drawing_ctx.rs
index 3a768274..72a4c18b 100644
--- a/rsvg_internals/src/drawing_ctx.rs
+++ b/rsvg_internals/src/drawing_ctx.rs
@@ -762,7 +762,7 @@ impl DrawingCtx {
         cr.set_matrix(matrix);
     }
 
-    pub fn clip(&mut self, x: f64, y: f64, w: f64, h: f64) {
+    pub fn clip(&self, x: f64, y: f64, w: f64, h: f64) {
         let cr = self.get_cairo_context();
         let save_affine = cr.get_matrix();