oc_obt:avoid double-freeing of discovery callback

Signed-off-by: Kishen Maloor <kishen.maloor@intel.com>
4 jobs for 151-add-user-apis-that-inform-the-user-of-the-ownership-status-of-a-device in 13 minutes and 9 seconds (queued for 48 seconds)
Status Job ID Name Coverage
  Build
passed #2126
Android_build

00:09:41

passed #2124
Linux_Secured_Test

00:04:44

passed #2125
Linux_Unsecured_Test

00:03:08

passed #2127
whitespace_and_doxygen

00:01:11