pci/hotplug/pnv-php: Remove erroneous warning

pci/hotplug/pnv-php: Remove erroneous warning

BugLink: https://bugs.launchpad.net/bugs/1862121
On powernv, when removing a device through hotplug, the following
warning is logged:

     Invalid refcount <.> on <...>

It may be incorrect, the refcount may be set to a higher value than 1
and be valid. of_detach_node() can drop more than one reference. As it
doesn't seem trivial to assert the correct value, let's remove the
warning.

Reviewed-by: Alastair D'Silva <alastair@d-silva.org>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191121134918.7155-7-fbarrat@linux.ibm.com
(cherry picked from commit 658ab186dd22060408d94f5c5a6d02d809baba44)
Signed-off-by: Frank Heimes <frank.heimes@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>