libsdl-mixer 1.2.11: fix libvorbis's search path

libsdl-mixer 1.2.11: fix libvorbis's search path

without that patch configure outputed something like this:
checking tremor/ivorbisfile.h usability... yes
checking tremor/ivorbisfile.h presence... yes
checking for tremor/ivorbisfile.h... yes
checking for ov_open_callbacks in -lvorbisidec... no
configure: WARNING: *** Unable to find Ogg Vorbis Tremor library (http://www.xiph.org/)
configure: WARNING: Ogg Vorbis support disabled

Then digging into the configure script made me found that:
  LIBS="-lvorbisfile  $LIBS"
just before the compilation of the test(the following output comes from config.log):
 configure:11947: arm-oe-linux-gnueabi-gcc [...] -o conftest [...] conftest.c -lvorbisfile   -L/usr/lib -lmikmod -ldl -lm >&5
 /usr/lib/libvorbisfile.so: file not recognized: File format not recognized
 collect2: ld returned 1 exit status
 configure:11947: $? = 1
we clearly see -lvorbisfile -L/usr/lib

./configure --help says:
  LIBS        libraries to pass to the linker, e.g. -l<library>
so I simply overwritten LIBS in the recipe in EXTRA_OECONF

The result was tested on nokia900 with wesnoth-wvga:
Before it couldn't play its ogg vorbis music, and now it can.

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@no-log.org>