perf/amd/ibs: Cascade pmu init functions' return value

IBS pmu initialization code ignores return value provided by
callee functions. Fix it.

Signed-off-by: Ravi Bangoria <ravi.bangoria@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220509044914.1473-2-ravi.bangoria@amd.com