package/pkg-meson: always set b_pie to false

pipewire unconditionally enables b_pie since version 0.3.20 and
https://gitlab.freedesktop.org/pipewire/pipewire/-/commit/abe73c9146cd223b40b22581b1fd58bc044c671e
which will raise the following build failure on m68k since commit
a6d88d3b:

/srv/storage/autobuild/run/instance-1/output-1/host/opt/ext-toolchain/bin/../lib/gcc/m68k-buildroot-linux-uclibc/9.3.0/../../../../m68k-buildroot-linux-uclibc/bin/ld: /srv/storage/autobuild/run/instance-1/output-1/host/m68k-buildroot-linux-uclibc/sysroot/usr/lib/Scrt1.o: in function `lib_main':
(.text+0x4): undefined reference to `__shared_flat_add_library'

To fix this build failure, always set b_pie to false as PIE will be
enabled by toolchain/toolchain-wrapper.mk if needed

Fixes:
 - http://autobuild.buildroot.org/results/c258a2736661af8ea73abeda2503d8682e65f1e2



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>