MIPS/Perf-events: Remove erroneous check on active_events

Port the following patch for ARM by Mark Rutland:

- 57ce9bb3
    ARM: 6902/1: perf: Remove erroneous check on active_events

    When initialising a PMU, there is a check to protect against races with
    other CPUs filling all of the available event slots. Since armpmu_add
    checks that an event can be scheduled, we do not need to do this at
    initialisation time. Furthermore the current code is broken because it
    assumes that atomic_inc_not_zero will unconditionally increment
    active_counts and then tries to decrement it again on failure.

    This patch removes the broken, redundant code.

Signed-off-by: Deng-Cheng Zhu <dczhu@mips.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: David Daney <david.daney@cavium.com>
Cc: Eyal Barzilay <eyal@mips.com>
Cc: Zenon Fortuna <zenon@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/3106/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>