perf: Really fix event_function_call() locking

Commit 558abc7e ("perf: Fix event_function_call() locking") lost
IRQ disabling by mistake.

Fixes: 558abc7e ("perf: Fix event_function_call() locking")
Reported-by: Pengfei Xu <pengfei.xu@intel.com>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Tested-by: Pengfei Xu <pengfei.xu@intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>