i386: Fix signedness of hyperv_spinlock_attempts

i386: Fix signedness of hyperv_spinlock_attempts

The current default value for hv-spinlocks is 0xFFFFFFFF (meaning
"never retry").  However, the value is stored as a signed
integer, making the getter of the hv-spinlocks QOM property
return -1 instead of 0xFFFFFFFF.

Fix this by changing the type of X86CPU::hyperv_spinlock_attempts
to uint32_t.  This has no visible effect to guest operating
systems, affecting just the behavior of the QOM getter.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20190615200505.31348-1-ehabkost@redhat.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>