Fix semaphores fallback code

Fix semaphores fallback code

As reported in bug 1087114 the semaphores fallback code is broken which
results in QEMU crashing and making QEMU unusable.

This patch is from Paolo.

This needs to be back ported to the 1.3 stable tree as well.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Brad Smith <brad@comstyle.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
(cherry picked from commit a795ef8dcb8cbadffc996c41ff38927a97645234)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>