powerpc/perf/hv_24x7: Probe errors changed to pr_debug(), padding fixed

fixup for "powerpc/perf: Add support for the hv 24x7 interface"

Makes the "not enabled" message less awful (and hides it in most cases).

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>