perf/x86: Remove temporary pmu assignment in event_init

The temporary pmu assignment in event_init is unnecessary.

The assignment was introduced by commit 8113070d ("perf_events:
Add fast-path to the rescheduling code"). At that time, event->pmu is
not assigned yet when initializing an event. The assignment is required.
However, from commit 7e5b2a01

 ("perf: provide PMU when initing
events"), the event->pmu is provided before event_init is invoked.
The temporary pmu assignment in event_init should be removed.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Link: https://lkml.kernel.org/r/1618237865-33448-15-git-send-email-kan.liang@linux.intel.com