[782/906] gldownload: Use strlen() instead of sizeof(char*)

gstgldownload.c:846:22: error: argument to 'sizeof' in 'memcpy' call is the same expression as the source; did you mean to provide an explicit length? [-Werror=sizeof-pointer-memaccess]

gst-libs/gst/gl/gstgldownload.c

@@ -843,7 +843,7 @@ _init_download_shader (GstGLDisplay * display, GstGLDownload * download)
           break;
         default:
           memcpy (text_shader_ARGB, text_shader_RGB_gles2,
-              sizeof (text_shader_RGB_gles2));
+              strlen (text_shader_RGB_gles2) + 1);
           break;
       }