package/sdl_sound: FLAC support depends on libogg

For the flac package itself libogg is an optional dependency, but for
flac support in sdl_sound libogg is mandatory:
http://hg.icculus.org/icculus/SDL_sound/file/394e3ec86164/configure.in#l263



To avoid compiling flac when libogg is disabled change the if-clause
in this package to reflect the real dependency:

$ output/host/usr/bin/x86_64-linux-readelf -a output/target/usr/lib/libSDL_sound-1.0.so.1.0.2 | grep NEEDED | sort
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libdl.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libFLAC.so.8]
 0x0000000000000001 (NEEDED)             Shared library: [libmodplug.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libm.so.1]
 0x0000000000000001 (NEEDED)             Shared library: [libogg.so.0]
[...]

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