package/ffmpeg: Fix Kodi 14.2 compile

Removing 0013-add-public-version-of-ff_read_frame_flush.patch in
http://git.buildroot.net/buildroot/commit/package/ffmpeg?id=4d094d9eb4edba5b6c3c229a2c02da1427e43fe5
was a bit too early since Kodi 14.2 still uses it, so re-add
0013-add-public-version-of-ff_read_frame_flush.patch
and rename 0013-fix-ff-thread-get-format.patch.

When Kodi 15.0 is released the file
0013-add-public-version-of-ff_read_frame_flush.patch
can be removed again.

Fixes
http://autobuild.buildroot.net/results/1c1/1c12779e67ddc6d3dffbc1d2e5ebf9887ae721ca/
http://autobuild.buildroot.net/results/c63/c6301fc6f11204ee157a4f6a848dda9666cfb450/
http://autobuild.buildroot.net/results/e61/e6138bac331370b02af746e319ce8fd6fe51b793/
http://autobuild.buildroot.net/results/c3d/c3dbb01608debd1bf0af6acd6eb9de6d01424982/
http://autobuild.buildroot.net/results/e1b/e1b0fbc6631a0073d743705400460b8679b28a0f/
http://autobuild.buildroot.net/results/180/1803aa8bd62e4fc126d0a791456804bb9b036e6d/
http://autobuild.buildroot.net/results/d2e/d2e9571f5747e609eb4f9b64ac6ab99bccb92767/



[Thomas: remove SoB from myself from inside the patch, as I was not
involved with it.]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>