powerpc: Fix unused variable warning for epapr_has_idle

This warning can be seen in allyesconfig, and was introduced by commit
f9eb581c63b2acce827570e105205c0789360650 "powerpc: fix build of
epapr_paravirt on 64-bit book3s".

Signed-off-by: Scott Wood <scottwood@freescale.com>
1 file changed