package/ffmpeg: Fix compile error on arm4/arm5

Fixes
http://autobuild.buildroot.net/results/d7e/d7ea8db79210228103257b6a28fada38cca142cb/
http://autobuild.buildroot.net/results/ec7/ec71e4f16ee9106747dff5f15999cbd17903e76f/
http://autobuild.buildroot.net/results/be7/be72eb182eaccf0064a32c9dfc2ac1c0d6555506/
http://autobuild.buildroot.net/results/b35/b35b71e3d21394e7ca24f3b112d8a4047cd6c87b/
http://autobuild.buildroot.net/results/5bb/5bbc8b5cdcd99229a6813970293f98b044fc489d/
http://autobuild.buildroot.net/results/be5/be54e75c4171d1db0eaaaeb5f5df29751d7db57b/



[Thomas: update patch to indicate that it has been merged upstream,
and point to the upstream commit.]

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