xen/PMU: Log VPMU initialization error at lower level

This will match how PMU errors are reported at check_hw_exists()'s
msr_fail label, which is reached when VPMU initialzation fails.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Juergen Gross <jgross@suse.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>