pnpbios: fix warning if CONFIG_HOTPLUG=n

drivers/pnp/pnpbios/core.c: In function 'pnpbios_thread_init':
drivers/pnp/pnpbios/core.c:578: warning: unused variable 'task'

Signed-off-by: Erik Ekman <erik@kryo.se>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>