package/upmpdcli: fix static build issue

The spotify plugin requires shared library support and needs <dlfcn.h>.
Explicitly disable the spotify plugin when building upmpdcli in a static
context.

Fixes:
http://autobuild.buildroot.net/results/cb942d3c5f68959d6cbc85535ccff4a275369f91/



Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>