package/pulseaudio: update the condition on NLS

Since the BR2_SYSTEM_ENABLE_NLS has been introduced [1], the
NLS support can be disabled when BR2_ENABLE_LOCALE is enabled.

So change BR2_ENABLE_LOCALE by BR2_SYSTEM_ENABLE_NLS and while
at it use a positive logic.

Fixes:
[nios2]  http://autobuild.buildroot.net/results/b69/b69c347e2866a97cc2c5d4844d567c4448592d72
[xtensa] http://autobuild.buildroot.net/results/b63/b63fd204fe36200ed5de70fff23cb59cf2bc778c



[1] dc057d28

Signed-off-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>