RadosModel.h: TestOp: initialize comp with NULL

CID 1135939 (#1 of 1): Uninitialized pointer field (UNINIT_CTOR)
 2. uninit_member: Non-static class member "comp" is not initialized in
 this constructor nor in any functions that it calls.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>