KVM: PPC: Book3S HV: Endian fix for accessing VPA yield count

The VPA (virtual processor area) is defined by PAPR and is therefore
big-endian, so we need a be32_to_cpu when reading it in
kvmppc_get_yield_count().  Without this, H_CONFER always fails on a
little-endian host, causing SMP guests to waste time spinning on
spinlocks.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>