target-i386: kvm_cpu_fill_host(): No need to check CPU vendor

There's no need to check CPU vendor before calling
kvm_arch_get_supported_cpuid(s, 0xC0000000, 0, R_EAX), because:

 * The kernel won't return any entry for 0xC0000000 if host CPU vendor
   is not Centaur (See kvm_dev_ioctl_get_cpuid() on the kernel code);
 * kvm_arch_get_supported_cpuid() will return 0 if no entry is returned
   by the kernel for the requested leaf.

This will simplify the kvm_cpu_fill_host() code a little.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
