linux: Fix uninitialized variables

linux: Fix uninitialized variables

In file included from ../src/nvme/linux.c:40:
In function ‘freep’,
    inlined from ‘nvme_get_telemetry_log’ at ../src/nvme/linux.c:169:23:
../src/nvme/cleanup.h:24:9: warning: ‘log’ may be used uninitialized [-Wmaybe-uninitialized]
   24 |         free(*(void **)p);
      |         ^~~~~~~~~~~~~~~~~
../src/nvme/linux.c: In function ‘nvme_get_telemetry_log’:
../src/nvme/linux.c:169:30: note: ‘log’ was declared here
  169 |         _cleanup_free_ void *log;
      |                              ^~~

Signed-off-by: Tomas Bzatek <tbzatek@redhat.com>