[aravis] gst: fix const warning.

[Emmanuel Pacaud <emmanuel src gnome org>]

commit 79c18d6bf55c7887b46e7d1b7b071bb9ef481a61
Author: Emmanuel Pacaud <emmanuel gnome org>
Date:   Tue Jul 23 11:17:16 2013 +0200

    gst: fix const warning.

 gst/gstaravis.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/gst/gstaravis.c b/gst/gstaravis.c
index b956e1c..c414655 100644
--- a/gst/gstaravis.c
+++ b/gst/gstaravis.c
@@ -166,8 +166,10 @@ gst_aravis_set_caps (GstBaseSrc *src, GstCaps *caps)
        gst_structure_get_int (structure, "depth", &depth);
 
        if (gst_structure_get_field_type (structure, "format") == G_TYPE_STRING) {
-               char* s = gst_structure_get_string (structure, "format");
-               fourcc = GST_STR_FOURCC (s);
+               const char *string;
+
+               string = gst_structure_get_string (structure, "format");
+               fourcc = GST_STR_FOURCC (string);
        } else if (gst_structure_get_field_type (structure, "format") == GST_TYPE_FOURCC) {
                gst_structure_get_fourcc (structure, "format", &fourcc);
        } else