KVM: s390: Fix vcpu_load handling in interrupt code

Recent changes (KVM: make processes waiting on vcpu mutex killable)
now requires to check the return value of vcpu_load. This triggered
a warning in s390 specific kvm code. Turns out that we can actually
remove the put/load, since schedule will do the right thing via
the preempt notifiers.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>