op_amd_handle_ibs() should return 0 when IBS is not present or not defined.

Fix compilation warning:
 CC [M]  arch/x86/oprofile/op_model_amd.o
 arch/x86/oprofile/op_model_amd.c: In function ‘op_amd_handle_ibs’:
 arch/x86/oprofile/op_model_amd.c:217: warning: no return statement in function returning non-void
Signed-off-by: NJaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: NRobert Richter <robert.richter@amd.com>