nvdimm/namespace: drop nested variable in create_namespace_pmem()

Kernel build bot reported:

  namespace_devs.c:1991:10: warning: Local variable 'uuid' shadows outer variable [shadowVariable]

Refactor create_namespace_pmem() by dropping a nested version of
the same variable.

Fixes: d1c6e08e ("libnvdimm/labels: Add uuid helpers")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220607164937.33967-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>