package/babeltrace2: disable -Werror

package/babeltrace2: disable -Werror

Add an upstream patch that disable -Werror to avoid the following build
failure:

lttng-live.c: In function 'lttng_live_msg_iter_next':
lttng-live.c:1226:15: error: 'stream_iter' may be used uninitialized in this function [-Werror=maybe-uninitialized]
     int ret = common_muxing_compare_messages(
               ^
lttng-live.c:1198:38: note: 'stream_iter' was declared here
   struct lttng_live_stream_iterator *stream_iter;
                                      ^
lttng-live.c: At top level:
cc1: error: unrecognized command line option '-Wno-cast-function-type' [-Werror]
cc1: all warnings being treated as errors

Fixes:
 - http://autobuild.buildroot.org/results/ff41326f913e71f982b3d5cbaf054f8be47913aa

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>