KVM: fix sparse warnings: context imbalance

Impact: Attribute function with __acquires(...) resp. __releases(...).

Fix this sparse warnings:
  arch/x86/kvm/i8259.c:34:13: warning: context imbalance in 'pic_lock' - wrong count at exit
  arch/x86/kvm/i8259.c:39:13: warning: context imbalance in 'pic_unlock' - unexpected unlock

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: Avi Kivity <avi@redhat.com>