audio/pulseaudio: fix typo in SPEEX option handling
b1ecad53b0b32916e5db596b26334db8015e4299 introduced a small typo:
MESONP_ENABLED vs MESON_ENABLED.
This lead to the speex-option not being able to turned off.
Reported by: mord0d@firemail.cc
PR: 273100