ffmpeg: disable lzma explicitly

Signed-off-by: Nicolas Thill <nico@openwrt.org>

multimedia/ffmpeg/Makefile

 	--disable-mipsfpu \
 	\
 	--disable-dxva2 \
+	--disable-lzma \
 	--disable-vaapi \
 	--disable-vda \
 	--disable-vdpau \