src: Fix memory issue reported by cppcheck static analysis tool

cppcheck analysis tool reports the following issues when run on the
latest Cairo source.

$ grep "(error)"  cppcheck_error_log.txt
[src/skia/cairo-skia-surface.cpp:245]: (error) Memory leak: surface
$

The proposed changes fixes the above issues.

Signed-off-by: Ravi Nanjundappa <nravi.n@samsung.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

src/skia/cairo-skia-surface.cpp

@@ -241,8 +241,10 @@ _cairo_skia_surface_create_internal (SkBitmap::Config config,
     pixman_image = pixman_image_create_bits (pixman_format,
 					     width, height,
 					     (uint32_t *) data, stride);
-    if (unlikely (pixman_image == NULL))
+    if (unlikely (pixman_image == NULL)) {
+	free (surface);
 	return (cairo_skia_surface_t *) _cairo_surface_create_in_error (_cairo_error (CAIRO_STATUS_NO_MEMORY));
+    }
 
     _cairo_surface_init (&surface->image.base,
 			 &cairo_skia_surface_backend,