encoder: h264: casts slice_param->slice_type
encoder: h264: casts slice_param->slice_type

slice_type in slice_param is defined as (char *), but it is compared against a
signed integer. clang complains about this comparison.

This patch casts the variable.

https://bugzilla.gnome.org/show_bug.cgi?id=747312

gbeauchesne/gstreamer-vaapi,ceyusa/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,GStreamer/gstreamer-vaapi,CapOM/gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,GStreamer/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,ceyusa/gstreamer-vaapi,CapOM/gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,CapOM/gstreamer-vaapi