topology: Fix up build warning in topology_is_visible()

Commit aa63a74d ("topology/sysfs: Hide PPIN on systems that do not
support it.") caused a build warning on some configurations:

drivers/base/topology.c: In function 'topology_is_visible':
drivers/base/topology.c:158:24: warning: unused variable 'dev' [-Wunused-variable]
  158 |         struct device *dev = kobj_to_dev(kobj);

Fix this up by getting rid of the variable entirely.

Fixes: aa63a74d

 ("topology/sysfs: Hide PPIN on systems that do not support it.")
Cc: Tony Luck <tony.luck@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Link: https://lore.kernel.org/r/20220422062653.3899972-1-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>