x86: oprofile/op_model_amd.c set return values for op_amd_handle_ibs()

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: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Robert Richter <robert.richter@amd.com>