package/liblo: fix build with musl

Commit 2759ba03 (liblo: disable werror to fix build issues) tried to
fix the issue by passing --disable-werror, but this is not a recognised
option.

Instead, just fix the code for good.

Fixes:
    http://autobuild.buildroot.org/results/000a46954d0c6d3dbc4b4634a0d3a3c955fac679
    http://autobuild.buildroot.org/results/58cb834bbd69bafc5cb0f23c236919c609648c05
    http://autobuild.buildroot.org/results/9de1c2007818082e88d77572abf8ff8a72e01930


    ...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Alex Baldwin <alexbaldwinmusic@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>